In what ways is the word “work” as used in everyday language the k )hq-ym 0ojpg6 zea6rs .ga,8same as that defined in physics? In what w g.qhm6ej, ag0o8y-prkas)z6ays is it different? Give examples of both.

Can a centripetal force ever do work on an objec7+ djafug( 7l1zibch2t? Explain.

Can the normal force on an object oesu bqsmu-+ ,2il+m3 ever do work? Explain.

A woman swimming upstream is not moving with respect to t,f3dlsq q06me 70 ovidhe shore. Is she doing any work? If she stops swimming and merely floats, is wd0df 0les 7o ,vqmi6q3ork done on her?

Is the work done by kinetic friction forces al2vfm jw186dus+pw *g mr l4.ybways negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under t.1r +lypu2mfgw6 j8w*dsmvb 4 hem.]

Why is it tiring to push hard against a solid wall even though you arkal1+ogfs 938rbi y 0se doing no work is 139gk8srflyb+o0 a?

You have two springs that are identica4a omv9ugvl q, z7(x/pl except that spring l is stiffer than spring/avx7gz qom9 u, 4(lvp 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 bli.kdogc(1dlk 57d+4z*brqi w3 p jj4zock that is free to slide on a frictionless .k +jdwjcz473 lrii(5pgzd 14kqbod*surface (Fig.6-30). 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 yo,i1wxl 1v yjy:ur gravitational potential energy change when ylyivx1w:1,y j ou jump as high as you can?

In Fig. 6–31, water balloons are tossed fromxs -r:fbri (.o-nl9kn the roof of a building, all with the same s9 lo-xf.n(bn r:kis-rpeed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its gm-, zt:vy11rkclcj1fs- om 6 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 swing the largest angle from the equilibrium poso: ymm6rg 1--jk1fct sczl1v ,ition? Explain.

A coil spring of mass m rests o1yxwsv2 ;c 2vupright on a table. If you compress the spring by pressing down with your hao2wsy21 v vc;xnd and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from th 5/uzs6nv4x h) zdlq-ee ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball againzdx zhls6 q)5/nue -v4st his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top of a wha0c8u4f2 o+ticz rcjp r9-z-aterfall falls to the pool b8ifrj9p4 2zh tuczcr+c a-o-0elow?

Describe the energy transformations when a child hops -dd:hsbc rh/6wqjue3w- eu0 vo(p 2 2qaround on a pogo stick.

Describe the energy transformations that take place when a skier starts s7zcjy:db pa+1x4 dkqv7 c,mh /kiing down a hill, but after a/pcvaqmchjdxb1 47 ,7zyd+: k time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at thekns:xsemkq uvzk 9f9y*- .7s . top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (bn.xeukv7k9yfq :s*z.- sms9 k) there is friction (deep snow)?

Seasoned hikers prefer to ste ;i9 ks5adg 3dcl)qu(oa uxi8;p over a fallen log in their path rather than stepping on top and jumping down on the ot)aa9q ou 8(s5d ugid;xcl 3;kiher side. Explain.

Two identical arrows, one with twice the speed of the other, are fix2lu y1 bm to,-6jxg.xred into a bale of hay. Assuming the hay exerts a conxjlogx ub61t xy -m.2,stant 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) ignorivpp c/gzko,(5ng friction, and (b) taking frictiog vc(,k5pz /opn into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater)p q c,vgm.le(j 3uch;q22laa than its original height? 3u,qvqgce(a2j)m h .pc2;llaExplain.

Suppose you lift a s ssyrfgub81:2uitcase from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more co 1y82ss:rug fbmplicated 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 rather than the 1ds pr*vhqw-r8ej1b t 3 8pkn-work.

Why is it easier to climb a mountaie o31ii f*tt5fn via a zigzag trail than to climb straight up?*f51 tioiet3f

Recall from Chapter 4, Example 4–14, that,up;ovkk)w0mc* qcyr6opzygx 457 .w you can use a pulley and ropes to decreaswz ;*k.yxcu kpcy ovg w05r)7,mo 64qpe 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, using energy concepts.

  How much work is done by the gravitational force when a 228cmwl-k wf c9x4jjr665-kg pile driver falls 2.80 c69rf2 lj kxcw8j4-mwm?    J

  A 65.0-kg firefighter climbs a flight fgjl j(h qdb3 lh/w-f6cx;91o of stairs 20.0 m high. How much work is required?-h fl3 1 hg9lcf/oj6q dbj;(wx    J

  A 1300-N crate rests oq--k e e+rav0uk;y j:;uns:k eu.dyz +n the floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 23 : adey+. kj :er;n0vqs;e-kzuuyu -+k0 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontali8zxb.z jp(d,17fzcc v- 0u tv;4gcoe ly) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was (v v;g bdf u o4pcic0c8tz,zx.e17-jz0.50?    J

  A box of mass 5.0 kg is acceldh z;t0.a1ilq8yb 9u5ilzel3 erated by a force across a floor at a rate of for 7.0 s. Find the net work donee5h0ibzal8q ll uyd;31.i zt9 on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a taif rvzrr75 *m;ak)wh+ble. How much work is required to stack them one on top of rvfr7w iza+h)m *5kr; another?    J

A lever such as that s*z bz1up+5w)psjwu q2 n,ox+zhown in Fig. 6-35 can be used to liff objects we might notoup qpnsj+)2u, zx1*+w 5b wzz otherwise 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 accelef)c y9t tuho-(rating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.otf9cu()h - yt40. 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 acceleri xg(.hg3p)l uation of 0.10 g 3.lh gpgux(i) 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 lineax o c4 jpo k6kx+i6-i5zsx*-ozr 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, acting along the x axis, varies as shown in Fig. 6–36uq*e f ev1i (aanj1/9rn+qja7. Determine the work done by this e*rq/inf nujjq(1+91vaea a 6force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts inkz55j8y)mu/xfw 9 smt 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, wil9u8lqrz(g4 gth 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,k 0eu1uzfc(iz+ ue (*f by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop1 is. 8(n0(glfn vute kt0bsr7 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 tgbrv-jt:s0j f e0m6j-o stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from aoc-: f07hilpf bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed o:i-0fhcpo7lf f the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’ dqk)t x-y46mryq4) wus glove backward 25 cm when the ball is caught. What was the average force exerted by thq4 rk4 umqtd))y-6w yxe ball on the glove?    N

If the speed of a car is incz r;s :g)brd4tj+hef( reased by 50%, by what factor will its minimum braking distance be increased, assumihr)(z;g er+db f:s t4jng all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators me*hou h(23e6 wza5:ik rx2w0 ,w-thmc5bkfhdsasure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kis*ah rtuw edwk2cmf ob h 60-:hh53wki,2(z5xnetic 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 oyy/4ia+nh b2 cvpp4+ pitched at By the time it reaches the plate, it may have slowed by 10%.pc4+nbp o4/ h+2 iyayv Neglecting gravity, estimate the 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 someone who does 80. p9;t7 bxdvkxje 8/+imn1:fzs0 J of xfim e9/8 x+z;1n:tbs v7kdpj work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sing;29o fua0 kivble cable. Determine f0abiko 2;uv 9
(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 m7 g-ogzr 61lmvjycdy626-q w euch must this spring be gg zmd ry -l-6co6we7vqy2 1j6stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What qu2jm(+xm bs1hw *6g1qe62ahhr;go a l b-xs( is the change in potential energy?hjs gb1xmu2;sag mx6-l 1*hq6ar(+b o 2qw(he    J

  By how much does the gravitational potential ener,,w-auv*ht-s.wi aqx gy of a 64-kg pole vaulter change i hi *wwatu,.xsv--,qaf his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it su: djt)te4ht:2 lt6kz trikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stifftjku4:z)ht t:2 ed 6ltness constant of the spring?    N/m

  A 1.60-m tall person liftsa(-k /s(hg7xzg+v lc 95de 6fwm: owcb a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative to s6ahldmgg/w9b7 ocw k5vcx(( -: ez+ f
(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 startsl69 d3 tishcm2 at an elevation of 1600 m and climbs to the top of a 3300-m peak.c3is2 6dt9ml h
(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/ofh-iny+0 k-;7o7lb sg 8vtcpm hangs 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 the end of the spring, where - tok ;7gv0+y ih-olcbn78sfpwill the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzb 8od 33/j(as4 z+f6wy8whkfc6(g w skjt:j vxan, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall t k(o:6c+ tk8ws/bdzy vsw(ah3j 8xwfg 34j6fjree 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, slidehdw. g6ps 77,;rag dcas down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove upgju1zxy-s2s .k6i4 g5 zsjs:l 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 gravitational potenrls 6 wq:7sl;/ x/uk w)0av,vvl y-ygvtial energy without the aid of a pole. With what minimum speed must Fran leave y -v xal: ygl;/6r,0wk7uvwqsvlsv)/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 upsp2-beu ejc t u-zuio*k 6m:,6ward from the top of a platform with 62ijzeuue:bc m tp,u*k --o6sa 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 stiffness constant is 9)j,5 9xakuzh)gyl2t(t r0yjs dab 9k:50N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a bkktj2 )hrlgjx : az)ydu(50s,ay99 t0.30-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 theot m:+ 10lwwrs (p0qgt 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 r), from what mini ot+wrpmt l sw1q0:0g(mum height h must it be released?    r

A block of mass m is att-w9nd6v3x 3mjp3p g jeached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacemen3jwm -n39 ejg p6x3pvdt $x_0$ 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 cord bo f:xf- bw38gwhose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bux -bf:gfwb83o ngee 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 to0qh3 6tz l6ufn point 1 where it is released from rest. Assuming no friction, calculate tn 6fq30lu t6zhhe speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speei vu9+4tz 0vied 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 placejae-u m m-q72sd 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 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 pasesq- -mmuja27 sengers.

  A cyclist intends to cycle up a 7.8 txwyt6oj0 (+ike3h; x $^{\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 traveling4v hsymdv1.4jq)2si ui1juaw -zub 3qn1mr 89 95km/h in opposite directions, collide head-on and come to rest. How much s8qvij h j2.w)u3av r1m niqzu1by-4dm14 us9thermal 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 rpkv a )jti y2.xax/3d/eaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this processkia.xx3j)/td y/p av 2?    J

  A ski starts from rest and slides d/2 nj56cki8iwrx wk ;xpbb -uhsk9l*9c+r ;vuown 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 droppedbkph5 sgx -h);nz5q(yu7l g:6zh hl2 u from 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 toxke*2bxgu58 j 5 dpc3b a height of 1.5 m. xu53 *bpk2djg5b ec8 x
(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 pulledcyg*5(bl i- k2 n/wwfd 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 cryw(lc5wbdink- fg / *2ate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If td.x r+q*cqw- m l.;unbhe average force of friction is equal to one-fifth onb mqldw+-*q c.rx;u.f its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reachei1 .mk0,acv sps 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 l7bk2h 6n ecs px:pgn5r3*5ptrjvu 8;xight horizontal spring (k=180N/m) as shown in Fig. 6–40. It in7ep: 5t u3; g*kpb xn62p58rxj shvcrs noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block i .z,j tabuu*y5s firmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm.b u5t,j.yuaz* 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 shutt+u7)bvkk/4 pt n sljj2le 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 spee+4n/2ljkvs7t k puj)bd 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 -rb + 62rhhgmfa 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m abover2h-+6f m hbrg?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the j0monus99an4 average force exerted on the moas 49 0nn9jucar due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rppw111 166s eiu, uu+a/ uptqf ec8qzmest to 95km/h in 7.4 s. What is the average poweruqp,t+ afw61/si6 8eumc z1u u 1epp1q delivered by the engine?$\approx$    hp

  (a) Show that one British horsepuz6kkryj8di 5,e 1yz 4ower$ \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-hoursb-enhd 3:x/ fi.”
(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 r ot6l2e9xhyoe ep:s33)n*auj6f2y w slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what pooe)l e rn36y6e3pwyhf s u2: xjat29*ower (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 irtcr;cqh2g s;(.oc 9 tn 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 taketw-amlh) v7dmq-rm4 ;fl-qf, s 1.5 s, what average power f4m-lmh wr-l-7tqfm,d qa); vwas developed?$\approx$    W

  A pump is to lift 18.0 kg ofh2qrs, : i:by kxkc3:x water per minute through a height of 3.60 m. What output rating (watts) should the pump mix::sr3kx:h qk y2,bcotor have?    W

  During a workout, the foot .41jlw0(8(f fvbnkq/x fd fztball players at State U. ran up the stadium stairs in 66 s. The stairsf(1b0(jnfdw zx.f4 f8vq kl/t are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclistl*.bomu zu( +xz3ag3,o*gwhb climb 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 maximubu2,z gs- nqr* 8hj,krm power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces addnk2qj,* -zsur 8,gh rb up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to d.r+t,l)v ob sqrag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45,blv .stqo)r +?    hp

  A bicyclist coasts down a 7.057w wk dw(q .-fb-7n 5jbiqnib $^{\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 ha f2uz nw+4v3auve built “5mi/h(8km/h) bumpers” 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 bumfa+u2wn 3v 4uzper 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 sh1wfqnvc7g n85u alafd58z- 5xelf is 10.0 cm 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 s8uzfv nx 7lwga5c n158- qaf5dhelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’t(w:0xk 6ojb ) svgx)qs famous long jump (Fig. 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. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top oftxx): bg)ow0sjv k( q6 the arc?   m/s

  The block of mass m sliding without friction along v8,9 xitmsg 3rthe looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of ram9is v3t,x g8rdius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from a vz44an7ayb .uk)5aq yb c+0dfn 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 termiv.0 nyaf7ya qc4z)+4ku 5badbnal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixed (m70m4 puvwn.(g u: fwqFig. 6–43). qwupn4uwv7m 0 gmf:(.
(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 o9tnilcw4rn2m;- db f2f a 3700-m-high mountain. The climb is made in 5.0 h starting at cni r-4b2 fwl2tdm9;nan elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks 8e r dviebx1 l56/p7-c +yf+*zl dylonwhen 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 qyfnd7x* 6lg .wi03cnthat its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher,3w0gxy7c ndn.*6q f li estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a d,e.gve7 ahtq czeo5;1am at the rate of 650kg/s and falls vertically 81 m before striking the turbine bladqgv1c z .5oha7et, e;ees. 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 verticalb7reuiz -bjl.gt6(v qje) ii0g/ 7t7 u 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, b77 z7jgq ( eitbu-0ti)eiru.j /gl6vsix times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how high co2n zvf( 9gvc5zuld an 82-kg man climb a ladder if he were fueled by one barnvcv 2f5z( g9z (=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 fire h8xzp5)h jhg;9nxlu 1wj h,d*d 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 bathroom scale, the spring inside the scaf xzf :,s 6j,xpuxv+)oj*-l pmle compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jum,+xjm-uxfjp,o): s p*z f6vxlp 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, an, s9rnt-t d9a:h1fx r++ukwaj d swings out over a lake (Fig. 6–45).kut9ns9 x rdh, t1aw++-r:faj He releases the 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 distance of 5.0 m in 9,k1bgn v8eam6 wx 1ge6.s uvfms5:gl(.0 s. What minimum power output was used to accompggm(k:. a5se1v w6v6xflse1 ,8g nmbulish this feat?    W

  Some electric-power companies use water to store energy. Water pjdb 0po./03b 3tbonr is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy 3 ./bobd0np j0rbtop3 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 n*9i60 yrf ewlthe spring stiffness constant for each of the two resulting sprinryf e9l0*i6w ngs?   k

  A 6.0-kg block is pushed 8.0 m up a x*//nif:am ej+w ys0uskv p34 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 wid:+wczj+v dx:isbf 37pfn -t+ll it take to +pv:nf- z:3f bd+wcjd+s7xtiaccelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walkkvi4bbu1 6 jaas8d*m )s on anm8j d4kb1 aivb*ua)s6 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 a 500-kg rockuf;7y t1ubxm 22a dz+so:l.ivm1i 3w n vertically upward a distance of 500 m, what wvli zym a;ubtwm2osu f3:2d+in.17x 1as its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95kg/s (a) zyt) w c(60e9cdzj;ziIf this( c;)zzy6z ti0 cej9wd 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