In what ways is the word “work” as used in eve7cujm/6nw* p8z c/*fleezj q:ryday language the same as that defined in physics? In what ways is it difff z:meuj8/pqczl/ cnj7**we 6erent? Give examples of both.

Can a centripetal force ever do work on an object? Explain.1- m jn )evx k.ncuk(:;)zwihm

Can the normal force on an objectmqo7dd7 5:zg(s qs/yc ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doin4*q sv roi.z *q)/bpyhg any work? If she stops swimming and merely floats,sqoz yp/4bq) iv*h*r . is work done on her?

Is the work done by kt 7. k+tg69kngzshpf3a4 (wlkinetic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablespha kg74+f3gklzn9. (6 t twkcloth out from under them.]

Why is it tiring to push hard against a solid wall evenci,rt pfb+r9 icp0- 3kin0sm( though you are doing no r9+mc, sb cp003 ipf(n-i kirtwork?

You have two springs that ,f3k w-yzcaj. are identical except that spring l is stiffer than sprinc,.a3y w- kfzjg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block m;zpllw)o )m, that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a dista) lmmoz ),lwp;nce $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational poteniq g*/wa6 xbe*tial energy change when you jump as high as yq*b/6 xawgei*ou can?

In Fig. 6–31, water balloondy-c x j-qx9y4w4*o pes are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resispyedx9 yco-- *4xw jq4tance.

A pendulum is launched from a point that is a nnue : -i 2h8kj4ume4hheight h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward a4u:n28enekji hum 4h -long the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on af.iob(b , u5le1gqfk:eo4(htr1 vdz3 g u -cc: table. If you compress the spring by pressing down with your hand and then release-uqrd3v(cb 4t1fc: uh gofez1(beio ,5:.g lk it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the tt8bz;umfj 325ybqqwx2r n9( ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball b83;9q x2m5bqyrn tjz u (2twfback and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitationah17. rv;n,bfdm w p,brl potential energy when water at the top of a waterfall falls to the poo7nbfr, ,;m1bd p hrw.vl below?

Describe the energy transformations when a child hops around on a pogo sticku4p*tr9h bsyvo.f4 rh q,/ll*.

Describe the energy transformations that take 8iu 0g3i plxs)place when a skier starts skiing down a hill, but30gi8l x) spiu after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) sta 8:z3 6,n p f;bi/wxladefafq;rts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no fzffd; wl/n,q 8:6ie ;3xbapafriction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rathx.( r9hfpokw + 2(fx bo8cn0fmer than stepping on tocr 0ffbw8nk (9fxpo(.+o 2mh xp and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a b 9/a: butqc+.3juevikale of hay. Assuming the hay exertk3u/i:q9va tc.ej +bus a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of e.a7ss,uv go l3tp:b*wte/.nunergy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to betn.g,uu as t/es.olb pw 3*7v: wound up.

When a “superball” is droppe mff /8xgtp.dt*ez:8 id, can it rebound to a height greater than its original heitftxi8d z: p egfm*./8ght? Explain.

Suppose you lift a szamo-xep 5f.p n k5++uuitcase from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it tan k55-+ m+xzop.fauep kes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the im isbmxl2g.vcuy//7g . c n5:work.

Why is it easier to climb 5- ozy1 5,ymyzfbnjx1a mountain via a zigzag trail than to climb straight upx,myoybn y1fj 1z-z55?

Recall from Chapter 4, Exampnv :zlkuy 5 rd7qhi3,/le 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every me7z3hu / iny5rqld,k:v ter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when :jt*t;ehe1 21rrudkua 265-kg pile driver falls;etrt :djur1 1hek u2* 2.80 m?    J

  A 65.0-kg firefighter cli0foh 2)o do(sf1bzstysg7l9(mbs a flight of stairs 20.0 m high. How much work is reqgs h0ty 21 boz(f foo(dsl97s)uired?    J

  A 1300-N crate rests on the floor. How much work is required to move un1q4a 9-qt thit at constant speed (a) 4.0 m along the floor against a friction forceq qt9 ta-nhu14 of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did thy -d;mv k+ zpzx5u.0cvoa1h .te movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough flo .-c015v upzxkmy;zo dva h+t.or without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of s9ltar,sx1 kx kwhh5 29zvooj /)2ja+ for 7.0 s. Find the net work done on the box.zo9lja+ /hjsv t1ok5xr)h9xs, w 22ak   J

  Eight books, each 4.3 cm thick with mass 1.7 vu hz/to5:hli0j a bi:ba;d9fs(*z d5kg, lie flat on a table. How much work is requi jbbthiu/9i d0oh:zdz; asf:5la*v(5red to stack them one on top of another?    J

A lever such as that shown in Fig. 6 yjcu:, :do.qr-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output c:: yr q,.djouforce, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from acceh8t:jx-/c. gs5xc ue flerating by a man who is pushing back oc-8fcgt : x/hesx.j5u n it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to giv*dbpcufb960 q mh +ku :(hc 0ts/cypz+e a helicopter of mass M an acceleration of 0.1u* 6bp(t 0h yhm++pcsz0:k u f/c9cqdb0 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linear and wt +t ,:sda1pythat $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fig. 6–37. y wd22ocnyj4+ Determine the 2 yn4 w2yoj+cdwork done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts -k;t 84fmsiwh5n hcyq-/cly, in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen lj,g) r*e (z ,-)w9vzphltgopmolecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by whaie7qs d4 3,nopyv np/- j2k)sbt factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electrhr7ftejd/-o-ae/ t) c /+a yc2ug2vek on $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop absze4 z(6e ws.g:rp,c 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strprca+,xa35zj7,. tcl/f g rcwing exerts an average force of 110 N on the arrow owrr7 .pcf/+ ccx 5a, tla,zgj3ver a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelin7rrkr )wi(o1 ug 32m/s moves a fielder’s glove backward 25 cm when the ball is caught.7rwkor r(1i)u What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what facn hm4a+2tp-4 vc* tmzqtor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reaction-4*+2qtmczha4 vmn tp time.

  At an accident scene on a level road, investigators meadokrz h7-mnj5;5pt 6j sure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use-;k6 tr5h mjoznjp5d7 these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a m+7t x1,j*7o rj:n 4lnodg ruifass of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the prglju i4:,tn7fr +djonx7 o1*late and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who d jt c,ofrf4e-5,+r*xsmmc8s roes 80.0 J of works,- 8c,+r *fs jmcr extmof54r on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by ddtts *+lqb j u*t q9(n3otq7+a single cable. sotndtbdqq97j* tl+u 3(q+t*Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant,b:wq51yloo n : k, of 440N/m How much must this spring be stretched to store 25 J of potential q1::b 5lwonyoenergy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m rr gv (:a d-spzgtm;9y,tf2iw:b v;z*higher. What is the chansp rry*w f;gz-;at v9d:m g(tzbv:,2i ge in potential energy?    J

  By how much does the gravitational potential energy of a d9jkw0s1-c5*ju mfo2ij k7 ll 64-kg pole vaulter changi2ck7w jl djlm 5 s-f0uk9o1*je if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a hqi4 f2f:vq4 vj;ie l;:q6su znorizontal surface has speed v = 65 km/h when it strikes a horizontal coiq4ujzq :6;ef 4n; 2qfiivl s:vled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 dk) tjke0 7w/wm above the ground. What is the potential energy of the book relattd/)kw0wkej 7 ive to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevationmdm61ef d h-74hphf tx1y) 6ei of 1600 m and climbs to the top of a 3300-m -6xdf1ehye4m)1 f 7imhh6tpdpeak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a rulev5e).bfa.9 p 75b2x mfgr pymrr. The end of the spring is next to the 15-cm mark ofb 5.5mp .m9x pvrg7y)a r2fben the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running 0syaw.un x 3p5duh7q(m a a2ipaa6t*0 at top speed (5.3m/s) and grabs a vine hanging vertically fry.*0mia at7sqx2n uw ha3(p0p6ada u5om a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from r*p/us.8 otarm p0yh)pest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionless 28.02 c:h(y4 w fr7ae2zr vabi /.ngl3u7ww$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s ki -f3ynpdu )*nnizyu8i(m8e 2knetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 3e)nn(88p*yi-dyunfmuz ki 2 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top ,m8l1gld76xo ( p.wdajsdzg +qv:l o.of a platform with a speed of d(+z 1jalwvml p.xd.7og: l6sd, 8oqg5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass),*b;ub 3x dgw9jkk892vfybwr ml43s k1 whose spring stiffness constant is 950N/m is attached to a table an94b flrj8bdg ;v3k m* 39wbwkkyus2x1d is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped i2w f3n* kgvmej58ss9track shown in Fig. 6–39. If the block is to remain on the track, even at the top o89fg s3*sm52jw envk if the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the encrs n -e1htb31d of a spring (spring stiffness constant k), Fig. 6–40. The block is gi-et3c1nrb h1sven an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge l68 n* 0uc1cnslrd*ze. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total nd68e*1r* ccu0lnl zsof 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 where ijo5dc p8+m j/r zx:l7xhw 1awiz.e2;dt is released from rest. Assuming no friction, calculatewd o;j8h/ z1c+ mlx :i7px5.ed2ra wzj the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angnr lmet5;,;c xhun8n)le of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an elevator ep:z)i(: xmlh2yt r,zshaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers ) ix mlh: tz(2,rzpye:undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cvcp )wx(9top8)ne,t,/ q8x5kqhn voc ycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of m 9errn b/i/ (+:apvqmzass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced ip+inz(abmq rev:/r/9 n this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches theizy0rjth62 8k bottom with a speed of 2.2m/s How much thermal energy due to fytzjri28 k 6h0riction was generated in this process?    J

  A ski starts from rest and slides doien: -p n0 gf8hdy1.ime9. nhown a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above th8zugn:gef dfa(y xgk 0zr9nh((, -tk6e ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball fromj2c mf9 )fax6i4)y+en ; ydkpd a height of 2.0 m, and it bounces back to a height of 1.5 m. 9x)pd+i jnm d; 2ca)ky4fyf6e
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, startinfxs+y p il yfxu+3p5;+g from rest, is pulled across a floor with a constant horizontal forcpplf+ 5x+fuy 3;xy+ sie of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in1qntipwc.fte) : q8 3tp0 lp+q Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? Theq ti :w)0epf 1nq.+qptplt8c 3 distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the9khow/jpp u *, foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light+m(sjjysew 4 iu3)1 vg horizontal spring (k=180N/m)jiy3 e4usmws gj+(1v ) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attach;z74hfic9qvy ir9)(1w psc h 1ygefi9ed to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the sp )h1 ;q wii9(y1z7i4egf9yrhcvsfpc9 ring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the spac*55 nm rssjevpty;g(et3 -;kvci0m v1 e shuttle used a “glider” (mass of 980 kg including pilot) that wasyss- e;rv 1g0temkv5; tpv(3m5ji c*n launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story 929lf( g4pdkrc5 oarar tqkg01bl1 ;v window 16lr;ld90crb gkq1ofv1 gpat24k9(5ar.0 m above?    s

  If a car generates 18 hp when trave* 4r; y2qzuic0td:w 4mon/ xpoling at a steady 88km/h what must be the average force exerte0uyz4 xow c;d: iq2/t 4nrm*opd on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in +eh v9ud;c -sz h5w-6b5cmac y7.4 s. What is the average powemce6 5 +hwz ;u95sb dvyc--char delivered by the engine?$\approx$    hp

  (a) Show that one British hoi j 6/h0*rwicluq 6km7rsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowat- rsvo4dps.o 3yya3a (t-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 1 qh6 xa.s;+ir-vlwua65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep theu-wsi 1+x6.q;avla r h car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h? (q1vwtkmsf + ovfz5-d,2 njw 6$a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14:s( g ezks1tll:q ;sr7m/s If this motion takes 1.5 s, what average power was1 lsklr s;:tez:q( gs7 developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through oh,cl x(nv ftom qjy)854js:;a height of 3.60 m. What output rating (watts) should the pump mohc:n ; tl,s)j4mj8 5oov(xfyqtor have?    W

  During a workout, the football players at State U. ran up the stadiq7ebf gc5zv: .zxnaok5n s96 2r ooxg0j126cfum stairs in 66 s. The stairs are 140 mz6 jb.of 27oxknorf:cg x2az5s v 9 qe60c5n1g long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climvd :v4f5 yyk1nb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill can it cln/*txfx c9 d+mimb at a constant speed of 75km/h if the frictmt/ dxx+* n9cfional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a atd33879s+ yr-1 ;h:l a f wr; izbgawlfgsfa2310-kg box along a level floor at a speed of 1.2m/s if the coefficient of f9r7lgala3: ww3r2;h bsiasad f1z8f gty+;-friction is 0.45?    hp

  A bicyclist coasts datt7rqtp3g 3t 5 gf1/o/zkgi 7own a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” thatya z.spmn6) egmeg4+y/c t .k19i8xou are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of/1 g .pinc y8+e.gmaky46tmx osuze) 9 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the groundn:o69 wbrlexv039eye8 iy gg., and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cmygwyib3r x g0l.o vne:9986ee , and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–4pr*iy scnd .;iqrv7zl4 qjm35ui gj mtk-*(0*2) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was tvj zuj 4g tk.7q sirri*cyd q3(-mmn5l p;**0iraveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Fi5ospapty.q b t.9(g/0n iz68dixox b-g. 6–39 is to remx9y/ 8dt0-(. 5n pbgbsqaxo6i. i opztain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft wito)bipb9io1 gs5t1 r;ghout his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg ap rbotg5o bi9g ;11is)nd his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a xktda.6gj 4 jryz)b)v:tz54 dhorizontal cord of length L whose other end is fixed (Fig. 6–4rtvy)454g)6kx tj dz: z jdb.a3).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the tz0ta o/bw )/dj2+bk d1kt6c umop of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. / zm +o1ckt ba/bduk62jd0t w)Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above m5fv7fi mc(m (a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can rjh5/4 fy xygpzo7z4*move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate tyr jp hfz 7/ox*g454zyhe power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of rl*y 6-c 4n7 k4axe a5k(bftr2 .xybir650kg/s and falls vertically 81 m before striking the turbine blades. Calculate a.brk xl2*4y (bcr4rxyif 7- ae6k t5n
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular verticalf v.ykjetyg,dt 5-hur8jv7( ) loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as 7fve8jdr 5kyy -t. jt huv,)(gyour speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, hoz r- /k:nfkc3o 9iz4bmct8o+p w high could an 82-kg man climb a ladder if he were fueled by one bar (=1000f8-+kbc/zzroc mi p3ok:94n tkJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45j :h2o3iuaa4l5trved 4z9f 4d.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scal ofe+lmw6n8 jl3sf ,5o4jvcut + *4mgge compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a hei5fnuv e 8+ftg*3w4g s l,+mcl jj4mo6oght of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5 idnc(d:1/gk ebzq 8c)m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases 1/c( :e zindb cd8k)gqthe rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distaj 8e6zo7 dt3auy q9w b9ad 0tlfyzg0r:.q.mx8 nce of 5.0 m in 9.0 s. What o9 07f. lwubz 0.yqadytex:t q68r8 dg39zamjminimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped b /ih4npz3sx*f */x1mnaxqo cz,tw1g: y reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a h3*qi/x :1tznwfx n,4zsamx/o gpc*1120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant wp,j fbnqfq 30,vajwch -d/5+k is cut in half. What is the spring stiffness constant for each of the two resulting sprinj-q vap / 0wfc, n5+q,bdh3fwjgs?   k

  A 6.0-kg block is pushed 8.l kf4z4xuhct0 7uzzk8t s-o6/ ns)d 8t0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h t.bz0ym at.g-0 vr,dgx o 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75g..v,gzxr ytd0 -m0ab km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks nh7ia zj.s- x;on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadm- nh7a;izs.xj ill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg ro,et- n*w-diwp phah1.vrzs / 6ck vertically upward a distance of 500 m, what was its velocity when it left/id1p vpnaw6h*-et zs,.rwh - the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/ m wjyeq1 y1.to p0df+qh1q(6mhxq9s.s (a) If this water wheel is set up to provide electricity output, what is its maximum powerp0e1. 9dm fyjy+qhoq 1x6tm qhqs(w.1 output?    W
(b) What is the speed of the water as it hits the wheel?    m/s