In what ways is the word “workb 9 (cyorqso40” as used in everyday language the same as that defined in pqc0(o9sb y4 orhysics? In what ways is it different? Give examples of both.

Can a centripetal force ever do yqv9xl;o 8pr 3h 2t2slwork on an object? Explain.

Can the normal force on an object ever do work? epd k.t8 */1 nw*fielvhh( ,hwExplain.

A woman swimming upstream is not moving with respect to the shore. Is she doingz7i8 g wh ij3eced*)j/ any work? If she stops swimming and merely floats, is work done on herg 8zdiwe) j 7jh*i3/ec?

Is the work done by kinetic frictio l1kcf/b- b9e ef1xrj-n forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under 1kf-e1cxl rje f9-bb /them.]

Why is it tiring to push hard against a solid wall even though you i0v+0sop9bu1 :in 3e-c d o *(oubijkiare doing no work* jb:i0p d90( 3oco+knioe-ib iv1su u?

You have two springs that are identical except that spr+mp0qi813amh glw+h ging l is stiffer than springl3+a+ h1p0 g mwhgmiq8 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 horizo gp-n:e/k d -qu1n5qufntal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it :-1 uqekd ugnn5 pq-/fhas 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 qie z(v8j un q z30-3chvc7gh;does your gravitational potential energy change when yoze-i8q(7qhg3h n vz0;cvj3uc u jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with j lnn-a5m*gkn 36 ,zuet; s7rsthe same speed but with different launch anglese7nsnsng*rk6l, z; 53jt-uma . Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launchedgd 6u99a0zmpc from a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initialm0z96 guap9cd 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 equilibrium position? Explain.

A coil spring of mass m rests uprig+j;o4qcw hfz4vpe zy;;p7: oght on a table. If you compress the spring by pressing down with your hand and then releasec4 yo;w z4+z7p:qvo ;h gf;pje 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. 6–34 ; u,et4ra)kf 7z,mpjmvmqj/3). The instructor pulls the ball back and stands against the wall with the ball against himzp,4 m) , jkqafe/j7vmr4tu ;s nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potentdc7b; babd -g +o f5fl)*vuq.aial energy when water at the top of a waterfall b;+)fbb*.ac7q vdg5ol u-d affalls to the pool below?

Describe the energy transformations when a child hoph3 r98gtcc (u 8o+ndyrs around on a pogo stick.

Describe the energy transforms*d: lj8 ,dmyzations that take place when a skier starts skiing down a hill, but aftedj,zmdl*s:y 8 r a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of heig0gwzc r ki pd-7(+.kbght h and slides down. Does the velocity at the bottom depend on the kd gkbg 7.w(z+-ci0p rangle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to h1a)s ep1)9qlwcn. d;+avll qstep over a fallen log in their path rather than stepping on top and jumping down on the other side. Expl9) he .lqa+l;p nlqc1vas1)d wain.

Two identical arrows, one with twice the speed of wa02:v g(wyg w/v:zv* jy5p fnthe other, are fired into a bale of ha0a(wwvy2v: ygzg :v/*5 fp wjny. Assuming the hay exerts 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 penda i)nmhun:7 (zyjpd r4we;+1wulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatherm7p 1z;du a wenr+ i)yj4wn:h( clock has to be wound up.

When a “superball” is dropped, can it rebound to a heightq5uow.rrec h1 ,y/+ b.x:tn ev greater than its original height? Expqn. b5+v1.ehre/ryctw, o ux :lain.

Suppose you lift a suitcase from the fke:37 6ct g1vea a.u*n vo k,qx8z+risloor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift se cazrv1+n8k*:o ,7qk3 . g u6aitxveit 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 ;df3ovjoz 9+ zd -e ow45-dcdnrather than the work.

Why is it easier to climb a mountain via nh :4o(-+nvb 9hlfsrfa zigzag trail than to climb straight up?:v+h l4rns nb-(o9ffh

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropesjml)(: h w7umgy: ui):9,ag ocq;aiky to decrease the force n:acgklam:hu79:y)qwu,)mgo; ( i jiy eeded 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, using energy concepts.

  How much work is done by the gravitational force q gbp3p 1r9e2fwhen a 265-kg pile driver fallsg3 2pq9pe fbr1 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much1 ke2/o9tks6taeei(7(sdd9yjk9 ali work is reqo7s ky/di9i9sel j( e9dka1atke2 t 6(uired?    J

  A 1300-N crate rests on the floor. How much work is x .7ed65sqc u8b u.zyrrequired to move it at constant speed (a) 4.0 m alonguez87.ybdsu q. 56rxc 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 160-kg crate 10.3 2( ajf-gdnc(m m across a rough floor without acceleration, if the effective coeff(c-mn 2g(dj faicient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across ap(mtwbblu,62*-cg ;iav o2v b floor at a rate of for 7.0 s. Find the net it,wpv; *u b agbv2l-2mc6o(b work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fed z7ly 37yg2jlat on a table. How much work is required to stack them one on top of another3dgj 7lye z7y2?    J

A lever such as that shown in Fig. 6-35 can be used to li9 5-hgr h fbmsmcrb:;9ff objects we might not otherwise be able to liff. Show that the ratirc bbrs; 59m9h mghf-:o 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 keivecjeyd :xj(c)l g,.van9 0(eoa-i /pt from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction.a(:j0j) c ax(e iy,gi9c d/n-vloeve 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 g j*djek4 odo3.3 mzpq7ive a helicopter of mass M an acceleration of 0.10 g .jkpmqz3743d*o oe jdupward.    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 dm*l:tvw 3zbf5* hem 0iistance axis 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, b 9:xhib8j.qz/n9oajr l 2c1dacting along the x axis, varies as shown in Fig. 6–37. Determine t/ljjqx:1b9i h9od2 b.8c aznr he work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particlqarh ;9 s 8(qvn(l05.aylokore 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, wit0h eqo1d 6ossn, yc+1bh 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 speed increasedz/u wzaf7l og74fn6.ne4 *cos? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requireo mrge x,3kftp ik4090d to 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 stop zr5b3-ae8 u+n1ookyea 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from ay yf(5mn4 8hz 6ft(bdgdw3d ecne3:6v bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the a3ye mf 4(6: fnz6bdgtvn3( wcdh58edyrrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 3bk ps+)6zop u0h6ers( 2m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on)r0hsuo6ppsz b k6 (+e the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum )- xrfyn/2ad:, ,o.7 vq djqd ezhoep8braking distance be increased, assuming aef2,.pdoqo q hyxz ,rd-7j: /8dne)v all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators m la q:id8e5sy9easure 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 i 8ey5:q9adl sspeed 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 time it reaches the 5b1aev vx +cthc lc,6f(*wf1oplate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate anv 1vb xa6+fccleow c,t 5*1(hfd the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown strai wdkj1*w-dn p04s 7mbu/mno7wght up by someone who does 80.0 J of work on it? mwu 1w j mn0 *sddnpkob7-w4/7Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertical uij.1zg;-1mvl: jsf(j rlzy+ly with an acceleration by a single cablei-1.rjjy+1gfzvz ;su: (l ljm . Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, ofdp k2/da jcx2: u, rjaygkf9.6pw.1tm 440N/m How much must this spring be stretched to store 25 J of potential energy? .w 2,um 2x6kajr/c. akdt1fpj9d:gyp   m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the cndmsvwo/j2 q + : tzp-m*/ ehdyc6vf-y -r8q5ahange in potentimwnh*cf-p52 :q8je - d 6d y-zvs /ytmvoa+qr/al energy?    J

  By how much does the gravitational potenti)w 5pb6*ccaxy al energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m duribxp5ya6 *c)cwng the jump?    J

  A 1200-kg car rolling on 0e;urpq)8yc bvrwf);z +7 hnf 8u+vcka horizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is broughkhyf prvn;+u+z f 8w r7)cq;)bu ev08ct to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m above :2c ( y.pezjw 2ss8bck+ds f)bthe ground. What is the potential energy of the boyc+. bsc2ks:sb)j w 8(d2fzepok 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 au )t0d12u0beize hn (nn elevation of 1600 m and climbs to the top of a 3300-m z(0i0nu heed12nu b)tpeak.
(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 verticaiz:hok)t;d) r lly next to a ruler. The end of the spring is next to the 15-cm )rh :dikt ;)zomark 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:/szz *v zqap9 at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing u9aq /z*zspzv:pward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down ,nk:q 0*cs5 a-d (k frkjwx6kya frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionless 28.-1a9t 5zsr90zzwhc ru0$^{\circ}$ 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 vr5 r;1r 6 qgusoll;c xz6f.owd(3 3amenergy is transformed into gravitational potential energy without the aid of (m6d slcg6uzw3;v3 qaoo .r15l;rr fxa 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 of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward frc.rpy7 dsht6)om the top of a platform with a speed of 5s . ht76ypdrc).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 stiffn 98dy .f-ja2rp(y fvhcess constant is 950N/m is attachp fr2jf h.y-d a8c9y(ved to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slidesppv)qf :5u 9z57ejb t2x )j./jzognsy without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is .97f5g:jpbszj2zov/t e 5juq xyp)n) r), from what minimum height h must it be released?    r

A block of mass m is a.mu 1hx,8 -+dqk jeoocttached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initialq,em odoh-8 +j.ckx 1u 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. Sh6esoc xj jk2)zg/ .;jve is tied to a bungee cord whose unstretched length is 12 m, and faez;os c) gjk2j/v j6.xlls 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 it ismb8wr4 x59xwj released from rest. Assuming no friction, calculate theb4jwwm8x 9 x5r speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed hkn57 (pru x2zof 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 bott 4yt3ee+h10qb:fzu: ugqi 1xdom of an elevator shaft. If the elevator cable should break when the elevator is at a height h a f:1gzd:hqqy u u 1ite4ex0b3+bove 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 cycxz50pg ys 6-cdle 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 95kuvr1 (pnzt )5km/h in opposite directions, collide head-on and1nzrt5 puk v)( come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 mww;4vnb dx *6i high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to fricvxwn;4dw 6i* btion was generated in this process?    J

  A ski starts from rest and slides down a 2 nez o9,2m+0ipmxj6:h wyv lfz 9+g-hp2 $^{\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 abd dbj jbnshe/5c2128nt 0aa1gove 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 a hbt m ;cay) ks 6(a8qaja+5f/o;baons.eight of 1.5 maobc jotkaam;6b.yns /q) a5 f(sa+;8.
(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, start.., bs eomnft ey cbm /qb7c2rns+(38jing from rest, is pulled across a floor with a constant horizontal fobn+rcb/2 jf., . 7qbe(c em tosm8s3nyrce of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes po/b fi vxp (68tczabs;9int 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with (9avz/t;bsf 6xb 8 cipwhat speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12 8m s ;wwtcfz kn.tw*y1v-qq75m/s reaches 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=186s1bjc1f5pa4g + igec0N/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 i+pef 5c1bg 1 6csja4gposition 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 horizl uj**u8co+vau)wox /ontal 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 1) *u*w u+8c/vuloxajo8 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 the space shuttlen/1jj+f*q0qgld pku34- vp rd 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 have bukp0j-pg ndq1q/4r+3* jl vdfeen in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg pianoqgd4w o (xhpdjn7;a 5: to a sixth-story window 16.0 mwq d:(xpnd ha7;5 4goj above?    s

  If a car generates 18 hp when traveling at a steady 88ko/(eo zy.al4k m/h what must be the average force exerted on the cae( zoo/. al4kyr due to friction and air resistance?    N

  A 1400-kg sports car acq:j wzf *n*0y)d3(zsfu)drjktj h j-5celerates from rest to 95km/h in 7.4 s. What is the average power delivered by t dhs:fj0t)ju)-(*df*w3n jy q5zjrk zhe engine?$\approx$    hp

  (a) Show that one British rn6lz;8;ef( )n8x dqwr/zzvohorsepower$ \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 avi5(2 cj.i cuare often expressed 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-kg car slows down from to 65km/h in abou0e3lxx x q1bfx36qk-g t 6.0 s on the level when it is in neutral. A0fk3xqe6q-l xx13xg bpproximately 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 6bf 4:r+8oaqxj9g;/kwn n;lwv oi6 toin 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion takes (c dm4niy7-c7.o dbb/tlvos6 1.5 s, whn/ dm ( 4tcbo.7ysl6o bdiv7-cat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height ofbg/ygr.rs/o.mg bta1 lg80i:im* ,jl 3.60 m. What output rating (watts) should the pump motor haveggl.0ojtg1 /gr rb.mlyb/:ii*asm, 8?    W

  During a workout, the football players at State U. ran up f)7ag ajv(y/93sy wzs the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle ofag s3jv() sy7f /yw9za 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 6.0 j 3cw)jbe4k5jlj*+t u $^{\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 stewav2y gt :4l,eep a hill can it climb at a constant speed of 75km/h if thelge 4,vyw:at2 frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box hf,q368x7dh 1b r zotdef y 7qju2mb20along a level flobqoq 8r2j t,6 0z2e f7mh3uyd h17fdxbor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts d55z2cm/pn 2gcm.ddc;7viy 84lh v iusown 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 designed to(o6j rc 0w-dzo;2v edv compress and rebound elastically without any physical damage at speeds bel2-j v0dvd6(co;row ez ow 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 0by6ybyj *iy: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 thejyiyb: b*y6 0y 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 tryqc. h v/;mjg+. duq5he 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if hjqg r5hc.my+;u dq/.ve 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 track shown inhd9j lt,dtseqj-o e30h h)* rqg ,m*9p Fig. 6–39 is teloqr*hpg hm h,qe93j-)*st9t0 jd,d o remain 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 jugl9r fbgh(j9q(7)plumping 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 was 35m/r7g fl)qb lu(9(hj 9pgs 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 .*rbf8k f+b 9 kpm7dj04ktu se*a1edw3b s) viend is fixed (Fig. 9*+ wd ksae8*t)ki redbj4m3s bkf7pf 0v.bu1 6–43).
(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 thbu6ly *ncxaix: : ,t6ie top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Cab *::tax 6lu, c6ixniylculate
(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 break-iw4qklbf ))a s when a 920-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 that i)dt4bg kj dz0t+uq z/*ts lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power ne0+d /z)k dqt4 bjgutz*eded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rats q/* a5fx0zi1veaa5cj1c fm/e of 650kg/s and falls vertically 81 m before striking the t1c0/cvq i *faazfmxj1 /s5e 5aurbine 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 loop (Fig. 6cdxbi6m3egd6 z.u,-x–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 fri m6bed3x,xz. i ucgd6-ction. 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 directly intop z 3af)sz9d j-ysq 00ava*s3b work, how high could an 82-kg man climb a laddfjq p)ssa0* dy9-3 0v3zzsbaaer 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 ap iqxp-b2+hd; 6s/y x14xcmv in 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 bathroom scale, the spring inside the scale compres3apfx1 d2pj71pb2 pzp ses 0.60 mm, and it tells you your 7p13zap1x jpb f2ppd 2weight is 710 N. Now if you jump on the scale from a height 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 over a lake (Fig.3w3hb n7 fe mixk4l5;,jgx4bb 6–45). He releases the rope when his velocitykhxb;5 4 4eflwbxgbjm,7n3i 3 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 q);w npt- tmhxz1i 9x 5s8w1 yasv-*f*d) kvisa vertical distance of 5.0 m in 9.0 s. What minimum power output was usedxfwz) it9-q dh;w savnp)tv*ixy*8-sm1s1 k5 to accomplish this feat?    W

  Some electric-power cof ,p*syyz dr )k89wo-pmpanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservo)dzf8k,- oppy*rwsy9 ir. 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 is the spring st6l.f-8dcjmvn iffness constant for each of the two resulting sf .vc8mj -l6dnprings?   k

  A 6.0-kg block is pushed 8.0 m,r0 wkcp1j5g2;lhe 08oj xlb6swg a, e 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 i/p yi i)*5x2(vhwiysin 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume t )(x*h5 2i/v yiyipiswhe power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the deg,*ansjf h n- l6b ;7xiy,h3patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at ayh;ns 3x hjfl-7*,,eb6 iangdn 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 up6 okj/;ftc ki8ward a distance of 500 m, what was its velocity when it left the volccjtfk/ 6ko8; iano? $\approx$    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 (a) Ifl1 ,4vl01uk yw 9uhxdi this water wheel is set up to provide electricity output, what is its xk0uwhi114yu9,ldl vmaximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s