In what ways is the word “work” as used in everyday language g(txw qfo99:ethe same as that defined in physics? In what wa:9gxfe9qo( w tys is it different? Give examples of both.

Can a centripetal force ever do work on an object? Expl,cn3 m5scftq2 ain.

Can the normal force on an object ever do wof e/p6c9 d-epabd/uhhej7 3o7zx2y7 mrk? Explain.

A woman swimming upstream is not moving with respect to the shore 1um r )w34njouc6az:.-wxz sm. Is she doing anyom1u u34)xznrm.w6 z wjcsa- : work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative?o), f9 rox+ff+)qduec,aa 6re [Hint: Consider what happens to the dishes when you pull aceaa+,of f)9o+, qfxd 6re r)u tablecloth out from under them.]

Why is it tiring to push hard against a sabk 6yx t/sbb b7cg4+ip6;2q bolid wall even though you are doing no b/i ybq +k4x6;scbp2g b6ta 7bwork?

You have two springs that are identical except that spring3 t3m*zqrzp 8 )sevklo::gn-b l is stiffer than sprmpvk 3s-:gre3zb)8loq nt *z :ing 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 that i:ro / :8b;ekh;hlc hjvs free to slide on a frictionless surface (Fig.6-30). The block starts from rest atkehv :or8;jc;b l :/hh þoint A, and by the time it has traveled a distance $d$ 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 potential energy change when9guj jt8w 0/2x 4vp.luvrg s;h youvj gtx; 0jup4. ul9v/wrsh8 g2 jump as high as you can?

In Fig. 6–31, water balloons are tossed fz ts8)(woa,sy rom 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 res()atzso ,8w syistance.

A pendulum is launched from a point that is a height h above its loweyrklom-yk3k8 cl(8il7 x5/rjst 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 along the trajectory. Which launch will cause it to swing the largest angle from the equily jomkciy73(l 5l /kkr88xrl-ibrium position? Explain.

A coil spring of mass m rests uprf69z *z+npgoj+p c u; njyp2 2xj+ro+light on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the no+upjg ;z+*z2jo lrf9 p c+pjx +y26nlaw of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (F +s- 2blsdu* g0+/k2turtn6d atoycy9,x9egkig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball wid go/sl tyu-yscx2n* tku,9+g2ar 6tb9 de0+kthout pushing it. Why?

What happens to the gravitational potential energy when water at the top of a wau ox2+. nah*ffterfall hnf.uoa*+x2f falls to the pool below?

Describe the energy q+-g 03lbjo ixtransformations when a child hops around on a pogo stick.

Describe the energy transformations ths. hrid 7j e.hw0.jlp9at take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snwi h 0dp. 9l.ejrj7.hsowdrift.

A child on a sled (total mass m) staj7ej/c ;3ldi drts from rest at the top of a hill of height h and slides down. Does the velocity at thed7;/jdicje 3 l bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log)86(,na bpimh qy s7ji in their path rather than stepping on,bpi8isa m6qj) y7(hn top and jumping down on the other side. Explain.

Two identical arrows, one withot*3n q , u6gwlahraq;3r nunu2;, yi- twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetra,un-*t,r rqw6ia;uany o nl;3qu 3gh2te how much farther than the slower arrow? Explain.

Analyze the motion of a simple swp f4 h;mp85dbuu0vze:qbp15o inging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock hq z5 fv8 e:ppb1;4pouhbm0u5 das to be wound up.

When a “superball” is dropped, can it r uv/dhg. x:af *ipx(1am5upr9ebound to a height greater than its original hei*v r(1p.:/g5a ap umufxhxd9 ight? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do 3r2lf(4r8ijd-sre: 0w so*cgic q e ,eon 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 tl4-fe(reo8cji, er3d* :qs0grcwis 2akes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power nee gla5lx0 k/ 6qf4m*apsded rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to clim ),xp4azat+)++tf1 7vhivvkabua *eo b straight uzu+*) +v) 4haxa+b,kv 1 ap7oetifvta p?

Recall from Chapter 4, Example 4–14, that you can use6*t wd25 3rm hvqyxnf/ a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, ust vmwxyq6f rd3n/*h 25ing energy concepts.

  How much work is done by the gravitational forcekhb8b *w7ycv),ews g* g.*sc e when a 265-kg pile driver falls 2.80 ew)hec7wgg*bbv*yc8,s s.*k m?    J

  A 65.0-kg firefighter climbs a flight of s7kk9 ltp2au 3ptairs 20.0 m high. How much work is req729tkak3uppl uired?    J

  A 1300-N crate rests on the flokfi t ces14v**or. How much work is required to move it at constant speed (k4 1sf**i cvtea) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did t( 9 xp::vzl2ev52mmxf8bn l aahe movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wa:blanexxp5 mzml 9:( v vf2a28s 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor ard 8 ,8gf2iqhlt a rate of for 7.0 s. Find the net work dg8,r8l i qdh2fone on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. f (uc c+ wdzd4fxvt lh-5-l5t6 yv/k;oHow much work is required (ot-y-5xuckc/ f6tdlv zvf; +hldw45to stack them one on top of another?    J

A lever such as that shown in Fig.cdb1e 03g lnnyr )q6:t 6-35 can be used to liff objects we might not otherwr1tb)ne ygqd:30l cn6ise be able to 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 acced7 sd( :qqd(zllerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The eff ql(:q dsddz(7ective 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 an accel hu0kbqrz9jt28p-- pl eration of 0.10 g hpkbr9quj0t-82-lz p 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 axu nyj)1o) cy ju0fj+ul51:y-db nu a(fis is linear and that $d_{\mathrm{A}}=10.0$ 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,7w y8o mk1a6do 0kgw.og*c 9en acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10wg7 . moo kwd*n1gkoa69ye0c8 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 o9k /yb9)yke.h b/6efoair0 zdn a particle acts 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 oxylu;lq )3)xo9awgy fieb+c ;o*r/+mqsgen molecule, 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 its speeevb5 l83dp.h*ih/*h 99f ri+gc chtold increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required ttvnm+bycz, pr 5j0-oz;6ax h;o stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 s+ rx944iui8g z zg2meztop 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 stringv+y2selzga6e6g 74 0 n/ vvned exerts an average force of 110 N on the arrow over a distance of 78 cm. Wzn20eg6sgv4/+vd 6ean 7l eyvhat is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelinpxv sslk23p6q9w h-* bilo, 0ar (tq8ug 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on 9tq(s6v urq0l2 p aks w3-h *i,o8lbxpthe glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum brhyznm)cjvs +w1ba :9;aking distance be increased, assuming all else is the same?j ms:wahznvb)9+;c1y Ignore the driver’s reaction time.

  At an accident scene on a level road, investigato:lq /;f* yig:ib hqb6trs measure 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 these data to determine the speed of qhby*:;gb/ftli i6:q 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 0.2 2uxrhw/fv /+p5 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate thex//f+2uhvp wr average force of air 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 someonem-v 1,1 p7pojf na*gdof-v rk9 who does 80.0 J ojdp7avkp fm*- g1o1of9vn-,rf work on it? Neglect air resistance.    m

  A 285-kg load is lifted 2 kx s6.yv np3mb4xh/kg743uez2.0 m vertically with an acceleration by a single cable. Determink ex /p7.n4skgmxv6 bh4z y33ue
(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, of 440N/m How much must this sprekz, eklq 7b l857dd9hing be stretched to store 25 J of pote5el8e7dz hb7d qkkl9,ntial energy?    m

  A 7.0-kg monkey swinc9xxwywm/ + +ymf23iz gs from one branch to another 1.2 m higher. What is the change in potential energyx3+9cmz+ yw 2 xmf/wiy?    J

  By how much does the gravitational potential energy of a 64-kg6q*m6 te*ozpf pole vaulter change if his center of mass rises about 4.0po6z ef**t6qm m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 6hbvoyolm xv).m+,w cy9 k,w;km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is th vwmov.m,k 6o+;,)b hclyw9y xe spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg bhdt8 j/dc+w pxwwd8 :ew3 3zj*ook from the ground so it is 2.20 m above 3wd*w+jx dj8c /:hwept d8wz3the ground. What is the potential energy of the book relative 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 elevation of 1600 m and climbs to the top oo*ix yn8 .gqb +u5zi76jqk)yrf a 3300-m pej y+q5 .6io*kz7 uyirnq8)gbxak.
(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 ruler. The end of)sfq66a ruki , the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end rsq,u6 i)a6k fof the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runnihhm f8q;b vs1q7y/0ddng at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungl0/fm d; yqdvsqb 78hh1e. 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 rest, slides down a frictilj frmek7 tk6 yy+z0m3xn( .*qonless 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 hkqhx omk .9ym5r/pswdz5x2 +urcjs;028bo 2 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 energy is transformed into x yr656t*w3z hvpvty7gravitational 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 th7 t yph6*y36vz vrxtw5e bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertica/u7:tudcfq i 9woa/a;lly upward from the top of a platform with a speed of i/7wcou9:;adfu a q/t 5.0 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), whose spring stiffness constant is fi0lev5 py hcbk976 s9950N/m is attached to a table and is compressed dbslk5 vefchi 69097ypown 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 ty1h:cp h,ymt8rack shown in Fig. 6–39. If the block is to remain on the track, th:8m1p,ch yyeven at the top of 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 end of a spring (spring stiffness cotb 5j;lndk (eq8jgz4* nv nci1u9*z5nnstant k), Fig. 6–40. The block is given an initiltn dc4z 5ju ge;*b*1 8kz(iqnv9jn5nal 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. She is tied to a bungee cordz; gxr7f6 ;zv6 vncgm fi)6bh0 whose unstretched length is 12 m, av 6nzzh7f)c0x 6gbmi;fg;6vr nd falls a total of 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.jya4oq.1lhvwpn ;) p ;:evtb* fh)4kl 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at poin nok;hlwh ):yqvfp4b)a1vj4;.pt le * ts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed ud.qqr:;) psj of 12 m/s at 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 designing a spring to be placed at the bottom of an elevator ,*c+ ir bv(xvqshaft. 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 undergo an acceleration of no morer* +(xc ,vviqb than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to ;aey ,y 93w1y uv:n whi3lbwr9cycle 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 mass 7650 kg and traveling 95k/l cww.ho 2hy7m/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this o7h /c2yw.hlw collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a speed +271pbtr uullb 9k( gwof 2.2m/s How much thermal energy due to friction was generated in 7tp kgu(l+9 1 br2wulbthis process?    J

  A ski starts from resc kb d+cjma.* c*9jbo*t and slides down 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 frx9nee0k os9we0c dbpy+66 *hxti8q 4mom a tree 13.0 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 to auq :o dbur)h)2o /aztyfjs:b.)9wfo 1 + k7jwi height of 1.5 m. ifw)d uyf21 7uo:).ooj9 )tjb hw+qbrka:/ zs
(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 pull+y6r rlz6pte3ed across a floor with a constant horizontal force of 350 N. For the first 15 m6+lrr6yz p3te 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 in Fig. 6–41 passes point 1 with a speed of If the s xuzex/+5b -javerage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance trbsz -xuxj /e5+aveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachdone8um 7ws0 3/s/ tuhes 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 ;yll :wwrb p83is firmly attached to a very light horizontal spring (k=180N/m) 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 tbwlr:y8pw ;3l he 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 horizo4ylhka) vcd + j95tly4ntal spring, Fig. 6–40. The block can slide along a t5)jl atckyv 9h4dl+y 4able 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 position will it stretch on its first swing?    m

  Early test flights for th1hc q.w.)lfxu e 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 eventually landed at a speed of 200km/h (a) What would its landing speed ha. .wfu)qcx hl1ve 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 motor4 u m-q*i0m5wdoa-, 2 wkojwpv to lift a 315-kg piano to a sixth-story window 16wvp *jdww-ko ,q50iomaum24-.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what musp7)w tf)v9tcg t be the average force exerted on the cag)ct97)tvfp w r due to friction and air resistance?    N

  A 1400-kg sports car acce-k))nstr1 :e.p*q;cubr 71sg et immklerates from rest to 95km/h in 7.4 s. What is the average power delivered by the eg -eq k; u.e:7)rntptms b*)ms1ikc1rngine?$\approx$    hp

  (a) Show that one British horsepo874bk lrva ( 4 u,j7tbo9wscet/;uftc wer$ \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 “kilowatt-hovf: a-0g e.mjfurs.”
(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-k xi3,s)ts es9hg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a con,t i9xesssh3) stant 75km/h.    hp

  How much work can a 3.0-hp moto g,u ++k*b3snykqcfg 0r do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7. zf0vdgze/ k) xag1k)33-kg shot from rest to 14m/s If this motion takes 1.5 s, wvf)daxkz) gz3 e10 gk/hat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through .b-vypj jd h6(a height of 3.60 m. What output rating (watts) shoulhjjby(p. d -6vd the pump motor have?    W

  During a workout, the football players at Statu q)z (eq:(glqe U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined qegul :q)z(q (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 clim ds6r(ic;dgsayn sj-a220k 5ewli2(tb 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 cli+t,i5 hll+ybp 6padoan5j1 v;- jr2gtmb at a constant speed of 75km/h if the frictional f2iy-h+ 5tljtgabp+o l5dj6p;a1nrv,orces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be ableu sd g 748e;ckzz) * -pj1fd4u:zdmayb to drag a 310-kg box along a leva4k1)u7e*u4 d;mzs dp cfd j:zbg-8z yel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down aa:o792-0 s ; if ewy,wiwzrbbx 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) bwxcx1hmy.x)hj sj /i1x6j9 7uumpers” that 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 1300 kg amh7ijxjxxwy6s/hx1 .1 9)cjund 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 ground :on;3cn0 qgad, 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 cm, and an average shelf holds 25 bo; cg30 naonq:doks, 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 (Ft5k 6 k ;vemfq x4t,dj(rp8,dqig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. j,f4t(5q k rdvx86p qt,;kmedWhat minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped ff5k u*,0ohkkp2 ku2vx1l4vbr g5 7jutrack shown in Fig. 6–39 is to remahfu 5 gpx lbr025v7 1fk*,oujkk4 u2kvin 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 fros po70rd+i9ol m an aircraft without 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 and his terminal velocity was 35m/s estimate 79irpdsool +0
(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 horizontal cord of length ppmlt (ja3q2 +L whose other end is fixed (Fig. 62ppa 3( tjml+q–43).
(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 ),y wk1hyu7 t9mh-4-7wst ehv, dkehz made in 5.0 h starting at an elevation of 2300 m. Calcuyeh dms7whh 4uv hk 7tzw)t, y9k-1,e-late
(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-nvac l.38d 5 6utbqj8hkg 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 thatjf.bi.4zs wd : its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertic.d:.is b zf4jwally) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s 00d iz)soifa8,5 emmd; 3vjqs and falls vertically 81 m before striking thd e qj;d3vfza,0im 0 smoi58s)e 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 ve; johm6rj8z )nrtical 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. Ignore6jzo;r)jhn8 m 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 convemw o4p0fq u; dr/ob1)srt a candy bar directly into work, how high could an 82-kg man climb a ladder if he;wu/bs4o1fomq r d)p0 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 firergho7pjdkg5y 3+40bb4( f vr3: y ogqnd at 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 bathro7g 2j lx1eq-jmom 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 heighjxmq7e -gj12lt of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out odmngqbg+5g 53)c4vt yver a lake (Fig. 6–45). He releases the rope wh53g b dq)tcy5g+4vmngen 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 distance of 5.0qlg2peg0 7 vn1 m in 9.0 s. What minimum power output was used to accomplisgvn2qel 701p gh this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by reve31k5-9i upjdt4mx qq8lfu (qi rsible turbine pumps from a low to a high reservoir. To store theq-m 9k8qjid(4xulup5i1 ft 3q energy produced in 1.0 hour 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-yxaax/xi nhvbw f5,c0m slre su1r0r)7-4x*. What is the spring stiffness constant for each of the two resulting springsx0wl1 -asx/ c* nmxve r-0bar5f i,4hysrux7)?   k

  A 6.0-kg block is pushed sn50bmcr z4qws) -og /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 from 35km/h to 55km/h in 3.2 s, how long will 6 zt8f1w2czsf phhl::f8l 4m rit take to accelerate from 55km/h to 75km/h Assume the poz:84l82trcl6 fh mffzh s1p:wwer stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walkzbw74gr5c6yio:nd l7 s on ow7iy4:r 7ldb5n z6gcan inclined treadmill (Fig. 6–46). 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 as ziznq,n.ts/ mcp,18 500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the vpti,1/n n sq8,m.zczs olcano? $\approx$    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/s kcd et8,v 6wa.(a) If thiec,v8kdat.6w s water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s