In what ways is the word “work” as used in everyday language the same asx8y m ndfo.5q *alwpw.bv3 .w/ that defined.f* 8www xmv/ayq.b.lp5 3nod in physics? In what ways is it different? Give examples of both.

Can a centripetal forcpq7uik98ms ( jjuxl 40e ever do work on an object? Explain.

Can the normal force on an object ever do work? Expl1u9fdt5rx+fj p 5e5 ig1:dhueain.

A woman swimming upstrsj3k.4f u me5l( d,gmf+qd0y5j-(h czlhvy9eeam is not moving with respect to the shore. Is she doing any work? If she stops swimming 5vl-+ emy(y5zuh3k4(gd0j9fcf,dl j s qe.hmand merely floats, is work done on her?

Is the work done by kineticd6,fk0wkbo v 2.b cwk9 friction forces always negative? [Hint: Consider what happens to the dishes when you pull a t,kw.wcb bkv90f o6dk2ablecloth out from under them.]

Why is it tiring to ba(egve39(:4rv mfpppush hard against a solid wall even though you are doing no work?4 9g3f:e(mvbp vpa(er

You have two springs that are identical except tl60lno5gr6b r hat spring l is stiffer than spring 2 rb5o 66ll0gnr$(k_1>k_2).$ 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 7ccyufo ;c q;q m/nydg/t*0 e:is free to slide on a frictionless surface (Fig.6;dn7:/ gce0f ;qq t*mc/ oycuy-30). The block starts from rest at 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 gra xg1i2(7 wpkvnvitational potential energy change when you j n(x17p k2gvwiump as high as you can?

In Fig. 6–31, water balloons are tossed from uuw7, r:r7hz q amzf-foq.:7p/txx2 3f4kndd the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed o7kq/x-af7zzu: ,w fuot r3 x. mh2fdrd:4pn7qn impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above it(g1h3erjpuq+ qsv6f.*oq i.vs 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 along the trajectory. Which launch will cause it to swrf*q qo.e.j6+gvu(h3p1vqs i ing the largest angle from the equilibrium position? Explain.

A coil spring of mass m res y knuk)8io1w ,b8z;omr,-wrbts upright on a table. If you compress the spring by pressin8 o ,y);ub1rizwr 8mk nbwko,-g down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The tmshozg9-i8z sud5vq18i7 ,1t3n wcr instructor pulls the ball back and stands against the wall with the ball against his nose. To avoidi1i 73smsutq 8dc- 9nt5z,zh or1g8w v injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravit2sdc -)2qj o pv*,kaukational potential energy when water at the top of a waterfall falls- k*pkd2vqc,u)asj2 o to the pool below?

Describe the energy tran 83did w 7yx*xv,uzsu2sformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skii /c,ex+zoa42 +0npdg3att(nf m +hs xang down a hill, but after a time is broughte( dz0fxa/+ n,+hsnt p+tamog 24c3xa to rest by striking a snowdrift.

A child on a sled (total mv0cy*5pa72 hcwm/ 2 qopc8a:l5hbewqass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angl 50 7wayo2p/ah 2lcqphm b5c 8veq*w:ce 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 in theirr996rn6zq8 p yf+ec on path rather than stepping on top and jumping down on the other side. 66neypn9fr r cq zo89+Explain.

Two identical arrows, onzcw078yoq mo z-im:z +e with twice the speed of the other, are fired into a bale of hay. Assuming the hay exertsw0zi7o cmz+8ymz qo :- 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 energy, (a) ignorin6xamn.f;bd 3h y psvx, )3h,lwg friction, and (b) taking friction in.;adwsxb,p hv3xymh6 ) fln,3to account. Explain why a grandfather clock has to be wound up.

When a “superball” is drop02zg ol 3x whub2r6te9ped, can it rebound to a height greater than its original height?g bhx69rz w0t2e2 3luo Explain.

Suppose you lift a suitcase from the floor to ap0llg grut87 0 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 pathl 0lt0u7g g8pr, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 f7.ao o) twovv5lmk5w4or the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail thaitu 5mv-ix ( )+z7nqgt6fzee1n to climb straight up?)ex6tv1 mng5ez(uq- t i+iz7 f

Recall from Chapter 4(5el7 u4 n8m(a-k r(qerrym rn, Example 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 ev r4-57 rqke(nanmey rulm(8r( ery meter 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 rluv,g36,fub.f yb r: a 265-kg pile driver falls 2 b ,ur,g3:f.6buy rlfv.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. Howw(f ,q ig4.3rp uu(qsfe :ptt+(kcp(b much work is requirf 4 3sq(f(ugk+ui.t pr: p qwec,(pt(bed?    J

  A 1300-N crate rests on teq+frdo ank+ 8fadum5 -(a: :whe floor. How much work is required to move it at constant speed (a+wa-ro(am:f85add :uf enqk+) 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 the movers do (horizontally) pushing a 1x dp:w.;a1tjl60-kg crate 10.3 m across a rough floor without acceleration, if the effect xwp;tld.a1 j:ive coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force ahrq uxp,0 z02cr/o:k pcross a floor at a rate of for 7.0 s. Find the net work done on the bp:k p,o xrhq2cz0u0 r/ox.   J

  Eight books, each 4.3 cm tev)+9-bxo6l gr84p ola .xmfshick with mass 1.7 kg, lie flat on a table. How much work i. 4gpevso r f x6ll8-+maxob9)s required to stack them one on top of another?    J

A lever such as that shokq- inh. +tage6x.tl-yt6 g e-wn in Fig. 6-35 can be used to liff objects we might not otherwise+h. t.-ni ey6q-6ttg ag-xekl 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 acz2 )lxptx7vgh+h1ax3celerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effvx3+zg p2l7 xh1a xh)tective 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 ofwx( fxp0t.hi) 3l/agjhy3f 1p mass M an acceleration of 0./x)1ah3 hti0y(x g .3fj wfppl10 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 thaq60-m 4vdzar p b-xk.ad 0sl;7)woohpt $d_{\mathrm{A}}=10.0$ 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,bqc l28ib*c)ufw c 8u0w2he o3 acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the objo8 ccic 2 wbu3w8uqb)h*0 2eflect (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 o3rxu9gpw -b79mb d/vqn 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 oxygen molecule, with masd dj1h;ml y::es 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 ik xh18zauj5b( ts speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to sto rqvndl6 4oo3gm07w yc*dj2 5gp 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 dov. e *)nxbicg1 w*wv:i80 iogwne to 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 force om5 jq, 6xtp9 mmb7+ypuf 110 N on the arrow over a distance of 78 cm. Whm 6u j9mpm ,xp+75ybtqat 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 backward 25 cmq jvo )crw.l:/a/cg ,t when t aqrt.gvj/c /lc)w:,ohe ball is caught. 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 factor wiln1tws:- /wtw5wpe byr4.w;psl its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reactionsbt. 4 y:/ww1p;esr-5twnw wp time.

  At an accident scene on a level road, inveshuan4ylvgdx, s ;1g7+ tigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficngv luyd g4x;sh1,a 7+ient 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 at By the t gogk22j v p:p6vd4p1aime 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 bet2pg pk2pov6:av4d 1gjween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by somka2pq.o i kh99eone who does 80.0 J of work on it? Neglect air resista a 2hko9pqik9.nce.    m

  A 285-kg load is lifted 22.0 m verti oy2z-m n- sio2hdw8v-cally with an acceleration by a single cabi m-- sd-2oovn2wh yz8le. 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 stiffnessg1o(.pl 1 yqqy constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energy? g1.(l oyp qyq1   m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Whaajzr2neg 3s:j5 g)s 0vt is the change in potential energy?z s5sagj j3envg2)0:r    J

  By how much does the gravitational potential energy of a 64-kg pole vault+ ) tn.sw)4f g-rvao rqt2sw8,jczt(ver change if his center of mass rises about 4.0 m during the jump? 48 rasq(zfo tw)jr twnv2g-,+vs.t)c   J

  A 1200-kg car rolling on a horizontal surfa7k2ga;i 9fwwwd+ lj fpi12 q;yce has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 i ;g27fp2ww9;djyl 1a q fikw+m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lift25.y jqwfnun 97h jx.zh1(asts a 2.10-kg book from the ground so it is 2.20 m above the groundqwxjath yf9( ns.h 1ujz .n572. 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 d67;kvsxf2ohgva8.wl xz9 7q*s )-b.spdvcy an elevation of 1600 m and climbs to the top of a 3300-m peaks wzg .-qd )ph7b o8 *7avsx 9.svvc6;k2dlyfx.
(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 han2r1y2/ mcbdog gs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to db2go1 cym/2rthe end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Ta 4qkbgbs5c-p2.q, vzwrzan, is running at top speed (5.3m/s) and grabs a vine hanging vertically frv cs,-w4qp.k2zb 5g bqom 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 rest, slides down a frictionless mfa-)d5:td y hl x *hekm- ih819,ugme35.0$^{\circ}$ 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 frictionlwfoup /7f dac5pr+u+cs) 3d)x ess 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 transa.c 4* dnnfa3hformed 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 macd3*nhf. n a4ass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verg8zo jdtupj2 fs )0- sb4jocl)*(7csl*h:xos tically upward from the top of a platform with-gs*4opc()lx: )7 sjsfo2u8 *hdtz0jblcs j o a speed of 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 stifa6duil.j49rx hrtid(h k:c1 .fac1h6fness constant is 950N/m is attached to a table and is compressed down 1urdtr9fj c:.6h.1 a hi6 lxhck(4aid0.150 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 track shown in Fwz,zyx0goh* a +1fr2aig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h goy2hxzw fra az,*+10must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness c 9r9pip5i 5jf)evqk5ukxc (3monstant k), Fig. 6–40. The block is given an initial dijkf5 m (c9q5xvk35r eii9pp)usplacement $x_0$ 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 t tkp7 g0d6gabj )6fox0o a bungee cord whose unstretched length is 12 m, ja6xgb06kgo7td)0 p fand 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. 6–41 is dragged up to point 1 where i0+1.1irew iorh (qm cat is released from rest. Assuming no friction, ca1mr.1c +(rqaw ieo i0hlculate 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 angli 410filr (427gx tad zpui,qde 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 desigmyo2 *)hcfakv0 /qes .ning a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value thatk*) 20/ mscqfe.aohvy 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 c. tx s(d(itd-aycle 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, eaejo/ -nptn /yo: x pde5mlr3/5ch of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much t//to5 mo/yn e-5dpj3lp:r enxhermal energy is produced in this 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 z0q0t 0r,d riij,rjp. speed of 2.2m/s How much thermal energy due to frictirj i,zd00,j q.ip0 rtron was generated in this process?    J

  A ski starts from rest and sliha6 2bhsgo*:mu dx9.rdes 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 from a tree 13.0 m above the groufnqh zy3jez8.1 d 2go(nd.
(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 a hepz )jnlffg)d ms9;j;5ight of 1.5 m. 5)pdm ;znf)gjjf9 ls;
(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 re;/bx lw lr*-zpst, is pulled across a floor with a constant horizontal force 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? p*l;lxzw r-b/   m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 rpgjuc8o0 m/b(y )n may /,hq4with 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? The distance traveled is 45. qc p04,m b(/r/u8 ajyohm)ngy0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot*9sw/y g7 jvs;m avq-o 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 veryer8 9bvltyu+ / 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 the equilibrium pos8eru9t v+/lbyition 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 horizontarev.u (ry+nf)0nk r:b l 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 equilibey0.k vuf:nrn)+rrb(rium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg inch*im9bpa b9m 6k.9g ukluding pilot) that was launched horizontally at 500km/ ug9k*mpbmb99a i 6.khh 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 -tnyf*pey/l +xwc) e9 to lift a 315-kg piano to a sixth-story window 16.0 m abovlcyxn/9-e+ p)te f*wy e?    s

  If a car generates 18 hp when trave*)xff 773qh zb31jovlcbw e+yling at a steady 88km/h what must be the average force exerted on the car due to friction and airyb xq+f3loh73 cz*e fvj b17w) resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whatt-ox)b,gmb (i is the avera,g)x(-bmb ito ge power delivered by the engine?$\approx$    hp

  (a) Show that one British. xh44 m(;bk5pxfq fav 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 expressed in the mthb 26o-pyb+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-kg car5x k)ju+ub *ys h/x(tq slows down from to 65km/h in about 6.0 s on the level when it is in neutrakyh+uu / x(xbtsq 5)j*l. 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 motor do p:m/g0k:6j wa.hjmj min 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from restyu s4 syo+p t/ p) r1;k:rak+zdgn5-w//pohb q to 14m/s If this motion takes 1.5 s, what average powezk ku aq:ohwdp-)1+5/ ps /tgr4+pybyr/ n;s or was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What o tc7bbi9p3- oautput rating (watts) should the pump motor havb3o t9i-apcb7 e?    W

  During a workout, the football players at State U. raj3p-q4/qn0 +r6 pbs alia6vdqn up the stadium stairs in 66 s. The stairs are 140 m lonl6- 4a3+bvsipqaq drn/ 0pq 6jg 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 cll -g5s48udwbpimb 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 iv)zk* ndlz,gj8p k1 6it climb at a constant speed of 75km/h if the frictional forces add up to 650 N 8pzj z,)1klvgk*ind6 ?    $^{\circ} $

  What minimum horsepoweroal r dmx19r(. must a motor have to be able to drag a 310-kg box along a ll1 ax9.mro(dr evel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts downaa(+: u, z3 43uqw*rexxoxswvonf0b *g0(yss 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” that are)(l7mb)u z-q/2y*kstwbsf fa 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 constanttkssfb z(2a/) q-7mblfy )u *w 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 cygg5d bs: e3f;m off the ground, 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 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to startd :5fes;gy 3bg? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fia 18bpo6q+qos d(/nu eg. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the t8a o+/q1 qbopseu(nd6 op of the arc. What 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 sl+w .jh yu,8yegiding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loo gy+yu8.hw,je p 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 felli,bf-6o1 oufmve 7r0pja l1 )o 370 m after jumping from 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-p)rmbi1ou ovo0,e7 faf1 j6 l 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 horizontal cord of length L whose other end is fixed (Ficvqx9e hx4gc .9jy,5kg. 6–43cj,5xykveq c9g9.xh4 ).
(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 z -y y2g8xeuj6me;7pmh1o /bu mountain. The climb is made in 5.0 h starting at an elevation ofbypy78xo; 6m-/1um 2zh jgeu e 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 920-kg elevator is 28 m above a hug(co34ad qi0w he 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 clafu 1uox 2,e,ckzz;d5 hims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the ;ode,,5zxfuku c1zh 2 power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at 8vcw ki)5am)x the rate of 650kg/s and falls vertically 81 m before striking the tuwxc k5v)ia8)m rbine 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 aj /1gwvc gkzxz22k;w7wu x 1,t circular vertical 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;71 gxjg 2v2x,zu1zkt/ckw ww. 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 bar pq:0tqo3tm5 6u yd hw6directly into work, how high could an 82-kmqut:ot 5w0 66yph3qd g man 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 at an upward angle of 45; ddmy rf9n2rluu hnxx(839g,.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 scale compresses +49ldpqxo. o s8u5ups *zj.ad 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 at its peaaq.s 9 o+8l5x uzou*4spj.d pdk?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fi(zjiubo +u v:e1w7p9 bg. 6–45). He releases the 1bw+vo(zube pu:9i7 j 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 distanaj n oo3(2/v .zaq kn*sipfx07ce of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat? qjk0(axs* 32 np7.i /zvoan of   W

  Some electric-power companies use water to store energy. Watervp*xv7f;bde //srjo i z+;av; is pumped by reversible tur/aj pvi;x fbv/ *s7;d;revo +zbine pumps from a low to a high reservoir. To store the 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. What isf)4ude/ e)ksv the spring stiffness constant s v )u)/k4deeffor each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up avv0 -1lw9kv qz 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 itr8pjc :4i vkk* take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictkkpj8 i:c4v r*ional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks hu9m 0hk7et ;won an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient w0ktwe m7h hu;9hen 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-kg rock vertically upwp3oh 2u94rtm6 e d2+gnfebd7i ard a distance of 500 m, what was its velocity 7ium ehbon rpd2+6ef9d3g24t 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 fr 9zj gtn(.2beqom a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output. ( zgje9n2bqt, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s