In what ways is the word “work” as used in everyday language the same assjj/fd9u b.3wn 1xo)s that definednjf b/dos j91 s)uxw3. in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do wojyx635h ywfv55n tin )-a4gem rk on an object? Explain.

Can the normal force on an object ever do work? Explain7jf08 jkgt6vljexx )vt;c 5 ;y.

A woman swimming upstream is not moving with respec9 x0h/ foaiw7z;t81wd dw -w4qei u9cnt to the shore. Is she doing n c/iw8-e9 dwxd 1zi0qw;t4 owuah 9f7any work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces dpesr)9tcy3i fw5 kd 97 q35rc 0*jhwualways negative? [Hint: Consider what happens to the dishes when s*p0qw)rtjhd cf3 9w 957i uyd3 kerc5you pull a tablecloth out from under them.]

Why is it tiring to push hard against a soliu6be(r(yh g.zd wall even though you are doing no y(uh 6erbz(. gwork?

You have two springs that are identical except th4,yyq:m9vl4de sa 7+vw q7iopat spring l is stiffer than spring 2 :l aw 7 iye,97ovpm+qyd44 vqs$(k_1>k_2).$ 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 that is free to slidta : v+v2wvja-e on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distvt: -+ajv2 wavance $d$ 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* ;03sxyr r6s q,phsleny u-bdwr2/f1 gravitational potential energy change when you j23u0-rrhy b wpxrf6/dn;l*ess y q1s,ump as high as you can?

In Fig. 6–31, water balloons are tossed from the ro/uom0b3i (vemls o1 .kof of a building, all with the same speed but with different launch angles. Which one hau v0.s(/ooe31limmb ks the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above it o-ybow.u;,s es 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,-eo.obys w u; directed downward along 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 a table. If you compress the jdx5*ia s0nd8n.aji*spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservationd* a ai*08i njjx.dsn5 of energy.

A bowling ball is hung from the ceiling bylc g4m*u 6pphn*e o,(b a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against* np* (,6obe 4ghpculm his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top ofmyco.xu,(c/uil nt5 ae ,(9d r a wa(/ xactiuy,.,dnrucm 59l (oeterfall falls to the pool below?

Describe the energy transformations when a child hops aroun +azd 5kqt*rs:d on a pogo stick.

Describe the energy tvjmbiu;t+ p2 ket2y49 ransformations that take place when a skier starts skiing down a hill, but after a time is broughtt4iy;b+9e2umjv t p2 k to rest by striking a snowdrift.

A child on a sled (total mass gd(8y1 0hboa8lgz9tq .)y evqvud 4v2m) starts 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 t. v1 qz2oly dqaybvhgv9gu) 8t(e4d08here is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their wv;:sk)s)a hl;eu vh4 path rather than stepping l w)shvh: )ska ;ev;4uon top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a(7j4oc.bb(ir/ zrcb c bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster 74c( ozbc(/jcrrb.ib arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of : i*rbdl +6)m5spmzmk a simple swinging pendulum in terms of energy, (a) ignoring friction, lmmsbi 6pm5d *:rz+k)and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” iyi *5jgd tc,r.a ejjv-9;ubq (s dropped, can it rebound to a height greater than its original height? Explta-9cur5.eg ,dbj; y i v(qjj*ain.

Suppose you lift a suitcase from the floor to a table. The wbk+:9nd is :ehork you do on the suitcase depe ki+bne::hds9nds on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rac (lc/sb. ug+pther than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb strailxe) tme,c,ak lc+ 7yh kre-6:ght up?lc6-ke+t, cmkr:e,ah7 e)l y x

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropesi /-jiv f ahoau4y (*2yug5lf: to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how mayf vlyai5(h*4og:f2 uj u i/-uch rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fahbb e44k 38+rgapu y0plls 3k0pab 4by4grhue8p +2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. Howjd jfez4**c.xs7 ;9n5gn jo o+go ao0y much work is requcx *o.gfa nn74sj0 eg59jyz* +odojo; ired?    J

  A 1300-N crate rests on the e.+/eqa3 m oy 6iwb*tsfloor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230*.wea i63oq+t/ysemb N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horiz tit*a2e*t(caz8r9mj (oq(chontally) pushing a 160-kg crate 10.3 m across a rough floor without acceljiterc* z(tah 2ta89o (q* c(meration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a flooe- pw2ui; u4qur at a rate of for 7.0 s. Find the ne4iqpu -w;2e uut work done on the box.   J

  Eight books, each 4.3 cm thick with rtfou;nzh 7+ev m8c32mass 1.7 kg, lie flat on a table. How much work is required to stack them onv8ozr t+3; 7m2uen hfce on top of another?    J

A lever such as that sa*ea;6dj0s sf hown in Fig. 6-35 can be used to liff objects we might not otherwise be able ta*0j6d ssaf; eo liff. Show that the ratio of output force, $F_{\mathrm{O}}$, 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 acccbcma3d7lv ; ch3 9*ilelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effec3bc hia*c7lc 3vm9;ldtive 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 give a helicopter of mass M k82 l.vt/ xnbpan acceleration of 0.10 2vp8/.nlbk xt 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 99nodh q hwq)8that $d_{\mathrm{A}}=10.0$ 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 objes kyq6ol7i/7qra .t; pct, acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this for6ql7 7pq;y/ra. toski ce 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 acg gs5 njy/.i3pts 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 molecu1p4f ml(zjgs(le, 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 what factor has it38x h petas(;i +.ftkcs 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 epor :w7q8re yh-zh 0z*lectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 1jvr4wq(8 i ia)yw ik*stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average f:rr bt t0.tt7qorce of 110 N on the arrow over a distancet:. 7rb0rttt q of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backn 8eaym265w c/ .nvslzward 25 cm when the ball is caught. What was the average force exerted by the ball on thsny2en56 zwc 8.m /alve glove?    N

If the speed of a car is increased by5iv,+ybg v4ijj-g (g c*mgsj/ 50%, by what factor will its minimum braking distance be incrgg5 +bmjjsv vg -(i4ji c,g/*yeased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a carb x+o tx4qz8d7’s skid mark to be 88 m 7xqob8dt4x+z long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use 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 mass of 0.25 kg is pitched;yjb5 lq/ f28ap 7vmfv at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of airyjf bq vvm/;82p5afl 7 resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by somhgb8ds1)c* qgl-e6* fgjw2g veone who does 80.0 J of work on it? Neglect air*c28v*gbjl ) g6ewfg-d shq1g resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration t:rr h ovj8-.a-iph n0 by a single cable. Detertj 8 vp-rn.ha -irh:0omine
(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, k, z bril,+k ill (j/)um-of 440N/m How much must this spring be stretched to store 25 J of pot-lblilzu ( rm+)i,/ jkential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m,j;)zl ad9j+i.l hioi higher. What is the change)io,;ijl i+d9. jlaz h in potential energy?    J

  By how much does the gravitational potential energy of ag1 ;hv/ dji.ka 64-kg pole vaulter change if his center of mass rises about 4.0 m during d/aig;1.h kv jthe jump?    J

  A 1200-kg car rolling on a horizontal surface hasvxy5j-byp1 zu8d4f /j speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spr 1bz /xjf5d8-v yj4upying?    N/m

  A 1.60-m tall person lifts a 2.10-kg book f3dimw ( scp*7evv*2 rirom the ground so it is 2.20 m above the ground. What is the potential energy of the book relative i7ew dv2v(rm*3ci* psto
(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 starts9,d nr3g2i izl-4duool vmpds0q,3alq9ce .7 at an elevation of 1600 m and climbs to the top of a 3300-m7 9.zi4dr, ooll0n2 siudq,cd9a-3 e vqg3mlp peak.
(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 iyjim jq/7ty w7-cb7c( -gh52*bfr qmnext to a ruler. The end of the spring isqijm w72 yjyhgbcbmr 7*f- -57c( tqi/ next to the 15-cm mark on 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 at top speed (53buqq qb)l;vdb bo-;6 cnis9bu- ;p l..3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How hibd9qb.3qov-;b- ubqclpl ) i 6u;bsn;gh can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slidewa5 nnc*3)c r 3r9uzuyuoe14cs 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 gi3ktr,jkf70 ) c1o;wuo nz8f dxven a shove up a frictionless 28.0$^{\circ}$ 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 kinetic en z 9c5y:+mduqy-g-zpoergy 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 2.10 m and cross the bar with a speed g-5:9zm-y c pouy+zqdof 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a plapfmx9 *k8f ,epavcl0 7 ryk5h8tform with a speed of 5.0 m/s.8fxv 89am 0*l7 frcyh 5ppekk, ($\alpha)$ 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), whose spring stiffness constant is 950)ud /ji3 ah sr,:bh.4frx5jwhN/m is attached to a table and is compressed down 0.150 m. (a) What upward spee,irr3jh w hs/afdjh4)u 5: x.bd 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 track shown in Fig5i1muff- m7gc . 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r)75 icmm 1ffgu-, from what minimum height h must it be released?    r

A block of mass m is attached to*sfne kj5zi4 c)tsxib8r14b 8 the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacemenki1jst5bb c )rsf*x8i z8 4n4et $x_0$ 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 kf +ds:7cfxv v3t9k9ufrom a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of k9v dc9k v+tufsx:3 f731 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 +9* vksvvnrje,wzz/nuf)p rx) l7(x 7is dragged up to point 1 where it is released from rest. Assuming no friction, calculv9 zz(j7,wnfs + vu /xrv)7rek* xnp)late 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 atq-krx/cg7i*ytdrbj ik6 0r 2 1 an angle 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 designinnr *e5yoc1 a;gg a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator isc5g*n;ya eo1 r at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers 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 cycle u oefc*h9e9uv5 p 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 mass 7650 8: z4 owxzamp7kg and traveling 95km/h in opposite directions, collide8 z4z ma7pwox: head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends ao*qxk dfp3m,/ j3mi h8ggs+ w 5xwkx/) slide 3.5 m high and reaches the bottom with a speed of 2.2m/s +gwm)3g3k/k j/sfm,8hxwd ox ip *xq5 How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides do; 3q4ppgl,lbh wn 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 13rkb2h29 pe/r.j5id4ou kad)e .0 m above the 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 from a height of 2.0 m, and it bounces back,g6j-8mpz lu )az 2lr-3z ibn-pkta+z to a height of 1.5 m.z,8p-tb )zm-rzi l 6ana+g -3z2 lkjpu
(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, starting from rest, is pulled across a floor with a constant zoryl- qcgpxkoq1 4t -1qrpc -u51-ap;p8e ) whorizontal force of 350 N. For the first 15 m theg 51a)1tl-r1 pkwp-q4cp pe xyqrc8;-uq zo-o 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 in Fig. 6–j2(v pkjgs*m 8-: cnkw n2wrl t3 oqd)lxd-:l541 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed wi 53:dk)t8n lr-:wgo* xv lmws n 2j-j2qklpcd(ll it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s rez..o/gcd1ih,tpj)ft aches the 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 horizontal spring (k= mmj jivr,mwf3n: 83/p180N/m) as shown in Fig. 6–40. It is noted that the blocj3 n:wmfi 3r8m,p /mvjk–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 attached to a very light horizontal x +zt1ocs*8 9bvbzzghxw7/:t 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 spring is released from this position, how far beyond its equilibrium posi*hgbc+v z bsx:8 w/tzto917 zxtion will it stretch on its first swing?    m

  Early test flights fo3ow6ud5k:vqr e8 r6*jg1 wejar the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider 1r* 6k:rd 5ju3vgjqe ew6 oa8weventually 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 liftjr+)r 4 znbfw*ccz //yuv/wm.p2l0f w a 315-kg piano to a sixth-story winj4zm vwz.lpfc/ un c/yb)fwr/r2+w 0*dow 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what mqs7 :pyr uu, 7:uyq/z,9 zxgegust be the average force exerted on the cqypx, gu:r u7zgz/y 9e,7:u sqar due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95kmdbtksh46 y ,l4/h in 7.4 s. What is the average pow6 4kbhsl tdy4,er delivered by the engine?$\approx$    hp

  (a) Show that one British zz-p 4i,u9v dv -5 egnapm,qd+horsepower$ \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 etu)qyr/p,/p aw7w jti bi5 0y6xpressed in the form of “kilowatt-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-kf1y3 wy762fe7 bvfd0tk4zn p wi5ru6cg car slows down from to 65km/h in about 6.0 s on the le0uv67wk5z7p4w bffc2i 1tf6dr3 nyyevel when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp,e5gv/cr36 zuiwemfh85un :9o i cs0w motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter acceler- srt0x x.09dspgvq(c ates a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average powe.xt9 -c0 ssdq(rxv 0pgr was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a heip2hn;qk l-t-xght of 3.60 m. What output rating (watts) should the pump motor 2lqn;-tk p- hxhave?    W

  During a workout, the footbad/o),(1 r- ddf oozdylll players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angfd)1 y,dodroo-/ z ld(le 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 climb a 5 z;fpe 9ct9du6.0 $^{\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 12ug5v w.n 3xzhb9mp9 m*0 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces addnvmbpw95m3 u*.hz xg9 up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg tu;s. 2ozjv,upso,kp 1)vyp3 box along a level floor at a speed of 1.2m/s if the coefficient of friction is ,; p)y. ps p 12u,jvkstvouoz30.45?    hp

  A bicyclist coasts down a 7:fu46qi ) vpbg.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” tha q*,ysg vm;i/3gk -vwgj+45g( kcuf let are designed to compress and rebound elastically without any physical damage at speeljvg+qcw54mik*f3gk- u;sv/( g ,y geds 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 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 theurt1ul 8m f(u.+mq rc6 ground, and the remaining four shelves are each spaced 30.0 cm above the previous on1(l+.tr8cq ruufum 6 me. If the average book has a mass of 1.5 kg with a height of 21 cm, 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. 6–42) in the 1936 Olympics sh xdf49msa8uvis ky5vs( ,jep 22 ub5.yows 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 traveling at 6.5mj4usy52(9b a8 xipvu ,s2e.m5syf dkv/s at the top of the arc?   m/s

  The block of mass m sliding without,jmj0mnm62r re 0ut o3 friction along the looped track shown in Fig. 6–39 is to remain on the trac e,ru2 06j mr0j3mmntok 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 w 6ibxq3n c y5f)llc g.+cmv7:lgalk+ (ithout 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 andg: n kx)i( llfqcm7+yg3c+bla .vl5c6 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 hfynz3 g48j5icdu 2 wg-orizontal cord of length L whose other end is fixed (Fig. 6–423zi8dnjw4g cu5gyf- 3).
(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 top of a 3700-m-high mountain. The climb is made yzg9* -1nbmzik:7cjjin 5.0 h startinjibz z m-*7kyc1:g jn9g at an elevation of 2300 m. 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 924kebs);xg4 x/*:yw zjk1wg yh0-kg elevator is 28 m above 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 thatgeys7gck j dpt7tg7b xc2/(0 - its lifts can move 47,000 people per hour. If the averagtc/gx7b7 j gpegc7 d -2sk0ty(e lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticallg-uk mr 7y/oyz2d*lddy wc b (*-3)ssvy 81 m before striking tuz2l dv-ck7g wm/ sbr-()*d yyy3*sdohe turbine blades. Calculate
(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 vertical 9tc ; e7b8nc4bnwo7jw, g4ezwloop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the n7,b;zn8t oeb4 wecjcww79 4g circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your 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 bab53p l (zt,u/lqq5 pikr directly into work, how high could an 82-kg matp5,ql plzki (/5bu3 qn climb a ladder if he were fueled by one bar (=1000kJ)    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 atrkq)zh- z*dx4 an upward angle of 45.0$^{\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 batyld6*twv8ms 9m b 72jjbzgo72 hroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read a6obm9*w7tvb js8mzl d7 2 y2jgt its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a tj lq1ip2.thmqmk)(m+b w y,- lake (Fig. 6–45). He releases the rope when his veloc jm-y,.)b wtpqmti1(lk2q mh +ity 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 clims ss f7hh b415g,a,xc* k6d-edqmskm; bs a vertical distance of 5.0 m in 9.0 s. What minimum power output was u-41mss shf75 ,;madksx6cg b*qdehk , sed to accomplish this feat?    W

  Some electric-power kj 4iyny *xh8/companies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 h8yhi xny* /4jkour by a 120-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 k is cut in half. What is the spr)tlx ixkvb8 h :79,wjring stiffneti k8jr) :xxhw9vb7l,ss constant for each of the two resulting springs?   k

  A 6.0-kg block is pushzi l8h1aoi6q t6bquz(2,o ycqu(u 9ote ,/vi-ed 8.0 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 fr,jkro- *)5 el*a w mgi0tdn 1rqpdd3o,om 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume th* od-,o 3*)dgdtep lm0 1,rnkr5awqij e power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient ;1iz2(udyvw 45econ xwalks on an inclined treadmill (Fig. 6–4d1 iwun o(4zvy2x5 ce;6). Estimate the power required from a 75-kg patient when the treadmill 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-kgkvyjk 6:a7m6i:j9fv gf qd,5 k rock vertically upward a distance of 500 m, what was its velo6a j7,d fkqv96j:mf:gv yk5ikcity when it left 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 ra xr)mvj;d g*dq(l ,ayt a3-:kte95y vzte of 95kg/s (a) If this water wheel is set up to provide electricity3aqldr,vg:; k9m - x)edzy*tv jty5a( output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s