In what ways is the word “work” as used in everyday language t hl jro byu/ezj )5tr3ya.)s7,he same as that defined in physics? In what ways is it/y jza s5jh t7you.e))3,r lbr different? Give examples of both.

Can a centripetal force eh-3yxnji. p p.w)xzc 8ver do work on an object? Explain.

Can the normal force on an objec3 2 tznn8j0xwdt ever do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doi-f/ i4aqh1j okng any work? If shaof1k/j- 4ihqe stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negat( xkpq(mi+d2yuy 1 e8w.. umcaive? [Hint: Consider what happens to the dishes when you pull a tablecloth out fumukiwd.y+xc(. 182 aq(ey pm rom under them.]

Why is it tiring to push hard against a solid wall even though yo,f-ob/ tkjmc p)-i9ltu are doing no workm)ci l-,/pt oktb-f9 j?

You have two springs that are identic vuasdrf8 ( i9u9j49fxal except that spring l is stiffer than sprjsd f9arxiu 849v9f (uing 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 am0(q.1- mafh oql;e+fu zzeab7h3hg. 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 has 7(bf fhlzo1h30aqh.m+ zaeg-;qmu. e traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change 1o3;jwa1w fs,b; 0*a3iu6 o u3uf,aragaatu z when you j atar1ufi,foaa ;wa3ow; 30jgs6u* au ,b13 zuump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, allmh fy54o4hft4 6e/ke k(4dqf l with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air lmfqfe4ho4f4/ 5y(kt6 4 edhkresistance.

A pendulum is launched from a pom5jwmo4oeutu c:k j( w;):2xh.n hzd:int that is a height h above its 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 pou:tow:j o(xm: j52w nzkh ;4)mu.hdcesition? Explain.

A coil spring of massj vunl4kkfl g.c)4 w., m rests upright on a table. If you compress the spring by pressing down with your hand and then release it, cannkjw4u.g .k l)v4f,c l 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 instruey8no (cx8fg+zm/)c fctor pulls the ball back and stands against the wall with the ball ac)mc/8nxge( fy+ofz8gainst 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 9a.+1mr n gqlfwaterfall falls to the+ ml9ra. 1nfgq pool below?

Describe the energy traa91 pckdfv,j0d 6kt3bq.v ;l snsformations when a child hops around on a pogo stick.

Describe the energy transformations that ta5o( 1 rjmex*5nt szy/dke place when a skier starts skiing down a hill,/jezr5 n5dts(mo *y 1x but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top sz0o/o,wc -yhof a hill of height h and slides down. 0y s,c-z owho/Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in theitml1m6)im+ iw)+ 9q;vqlct mxr path rather than stepping on top and jumping down on the otheq6l+t;w) qt1+im9m)xmvi mcl r side. Explain.

Two identical arrows, ozgha dpc(z9zm-q7 9 5wne with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate h9 wadgz cz5-qm97zp(how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingrz 98-tq n,/bmqm( orz7kvz2ning pendulum in terms of energy, (a) ignoring friction, and( kq-vo2r nmrtz9zq7z/m 8n,b (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater tha2zo-xy 1hh/llj -fvy dl:h4u-n its original height? Explain.2hlh f l -xvjo4--ul1ydyh:z/

Suppose you lift a sui31 + knqa/vfnutcase from the floor to a table. The work you do on the suitcase depends on whin ka f/+qv3n1uch of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather 1n6vo k( tb:hmuc3g4d d -nxl(hu 9s/7swdpq0than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb37xg4st o8kk.l7h(, q0gzphx r52xyze. ls r x straight up xz35 xth4 kz lq,k.g7(287g hpl0oxsyr.rsxe?

Recall from Chapter 4 oivdf1uh7/ol/9 (kur, 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 every / r(/kuudfol9ih1o v7 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 gravitaticzd:.ij3zk )r8 we1e sonal force when a 265-kg pile driver falls wjd) ckse:.zz83i 1e r2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How mu;3hwmf-z8+xexh cint s 4xc (3ch work is require4in-xtxwzc +(;sm3hch8x e 3f d?    J

  A 1300-N crate rests on the flsn-aiz39n g50 ngo3dv oor. How much work is required to move it at consta 3nsn5dn3i9-gv0 azgont speed (a) 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) px1 ebj6;my(k pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of frictiom;bxe6(p 1yk jn was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate ofozvl 94n8e/g f for 7.0 s. Find tnfv 4e8gol9z /he net work done on the box.   J

  Eight books, each 4.3 cm thick with mc 6dpif j 142- se1.ap9kfwmq7wdhlq1ass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of anotherka1.961efimqwc2dl 74jdswp- 1p f qh?    J

A lever such as that shown in Figm /f6;l )ti:lf gjrsur,75dep. 6-35 can be used to liff objects we might not otherwise be;5:fte6d )ufrjsmg ilp/ r7 l, 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 a2p- g w -gmj7wlpyepf/)-w8hu zcq)/znd is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction gp)g 8y)z-jwq h -p2- cf7mepw//wluz 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 requon()peib3kc *ired to give a helicopter of mass M an acceleration of 0.10 g up p(nbe3c) *koiward.    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 kg yfa6j6gni2zxaf p+8 - 5gr*distance 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, acting along the x axishe e(y)+uinb4, varies as shown in Fig. 6–37. Dn (u+4e)yhei betermine the 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 oniv- 6.u9 lcnfm 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, wh lprxbv6/4 +r poio1;ith 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 arrojeluo4:9s -k b gs8-hxy3, alyw is doubled, 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 stop an electron9vbt.mb)uy *3ontch) $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 a 1250-kgcar traveling at 105km/h?5. ubzklu w08lf5xj3 e$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an averagsm,;j)bf4n(igein - b e force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arfgn(s imbn- ijb)e,;4row as it leaves the bow?    m/s

  A baseball (m=140kg) travelinzotc1+xt tx* 3g 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. 3+ot 1cxttx*z 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 facoo26ibif /vw)ur/jh5 tor will its minimum braking distance be increased, assuming all else is the s wii)frv/j5hu2/6obo ame? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators mea z s1a/ji1bdp t5iy 44smztm)(sure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetimz1/(1sii adzmy s4 bt) 4tjp5c 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 0.25p5 x3cckn7u,d kg is pitched at By the time it reaches the plate, it m3 ,c dknuxc7p5ay have slowed by 10%. 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 bsl:- ok)x/1om4fz jq yy someone who does 80.0 J of work on it? Neglect air resistance. lj1-oomyx:q )z/ k4f s   m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a d+gt5mrmqc9yrg 98bj2*b gf2. zcs -osingle cable. Determineg bgq z9cs-92ocj852rgm ydtm+*rfb .
(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, k6psukqlv 3mjf21z 6m0*hwey/o2bm ut sg92) of 440N/m How much must this spring be stretched to store 25 J of potential enep3s0l2*uw 9/tvomkzg6 jk1y)se2mu2 m qf6bhrgy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m hi 49;+o+mt c cnfcqvwo-gher. What is the change in potential t +o-4cn+9 cwv;q fomcenergy?    J

  By how much does the gravitational potential energy of a 6462dagemb: l.a95irxsij9 s1 n -kg pole vaulter change if his center of masa rljn.6x d2ss5: mi9iabge 19s rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal s/ owt*h/q5 rhjurface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant oq/rjot/ 5h* whf the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the grou,zsnkkb67 6b lnd so it is 2.20 m above the grosb, z7ln6k6 bkund. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevatio-yh1 5 .6ci xagqxd:xa0)pum pn of 1600 m and climbs to the top of a 3300-m p:p- p)yxxh. aa gux6i5 c1dmq0eak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the tui;:c ep p7(alwfu/2spring is next to the 15-cm mark on the rui;ep c 2ufat 7(wup/:ller. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top.r hi tz454tf /w qmq2d3iik3v speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward3 z qrik2/4mq34ftwi 5htidv.?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, .ls g6c gz4k: gpuai9+slides 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 d ofz 2.6zyic0shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitatiour , 1yc6/wg0yl,;y3uj aao kgnal potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and ccua y3 ,glwyo/ gak,y0uj6r;1ross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps ve y6;ct3k4vxu artically upward from the top of a platform with a spee46utx3 yk ac;vd 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 cons9o9qkyr -d uk;tant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed cru ;9-9kdoqk yan 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 tra t/g9a-s+b kmick shown in Fig. 6–39. It/am+gi b-sk 9f the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is cd c wt63wd,(jy 1g/ru.ccx my q;mg55attached to the end of a spring (spring stiffness constant k), Fig. m(,tw./cwxy cj 5u16r;gydmg5 qc cd36–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whoc+dmi ex;4.f.wywq; f se unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of t+ c;wfdw.eq4; m. xiyfhe 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 jvoz )mnk49w+3shh0n ;fbn 4,qi rf1mto point 1 where it is released from rest. Assuming no friction, cal;f41oj iz3m,q)n4b f9m snnrv+kw0hh culate 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 ald/wnn p:m+9*s x0tjcngle 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 alrt/ig+pnd( f 9;c,j d spring to be placed at the bottom of an elevator shaft. If the elevator cable should break whennr +dcl9di ,tf;(p jg/ 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 passengers.

  A cyclist intends to cycle up w-a:qni6 gf7l tu ,u5ta 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 95km/h in opqp8),qqw x+npposite directions, collide head-on and come to rest. How much thermal energy is )qwn +pxqpq8,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 (h s6/hep 3doca speed ofo(6 sph/3e dhc 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slijb )6x5 6orsv azei(w0des 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 ground. v 3iq j,oo(wtp uay1kfy*z15,
(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 h; d((hvf,eb hjeight of 2.0 m, and it bounces back to a height of 1.5 m. v bdej ;,hfh((
(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 pulle -n :u:otlw6x2r/51ra sbfx ptd across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and fon2pt1l -u/r oxr 6f:bt:w asx5r 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 passfwx1:nmu:oqbfuo j1.*a b mp *j7b; ,xes point 1 with a speed of If the average force of friction is equal to one-fifth of itomf:j*aq1; jpwbu ob.xum ,1f*7n:b xs weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot yju1o:(ffi10noe 3it yal0s6 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 h qrzcq*p- .l.8zbsom-l7n 9k is firmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–s9 .8m*crl.ls-zhpk 7q nbo- qzpring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig2;7j fhovsncre y(o4j u:kh22. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses theyoj4 nus:h2vehcrof722 ;( kj spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” :7o6ypi+ah xv(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 been in the absencep+i hyv7 ao6x: 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 moto *x*- ar:kfgfzr to lift a 315-kg piano to a sixth-story window 16.0 m xf*z fgkr-*:aabove?    s

  If a car generates 18 hp when traveling atsd f7oow qcs/h1/ v;t4 a steady 88km/h what must be the average force exerted on the h1ws/47dvfqo s;o/ct car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km9zt v4l/khq8 gep(y1y/h in 7.4 s. What is the average1 8yzqvtpghk /le94y( power delivered by the engine?$\approx$    hp

  (a) Show that one British horsepkggko qmbi -w;*c)vi k46 7hs7ower$ \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 )y0y))a l bmpwfp-)x3arldyx;ov;m0form 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 sl, *w thf(e vm rpd0o8zm:55mdkows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to h5zw:m fd(*0 5v,opr8tem mk dkeep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h?h eppv-9srkfu*1 ,za 2 $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest *mwy mg2qj5fxzvcw5ss2. 4j1 to 14m/s If this motion takes 1.5 s, what average power was dexy 2jsgjw 512fcmmzsw4v 5.q*veloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height ona(n)jlh,i mty get;/(yw c*.f 3.60 m. What output rating (watts) should the pump .tay;t j eh*)mgnyl (n c(w,i/motor have?    W

  During a workout, the football players at State U. ran up the stadium stairs i/2 nxnzz+3pn+fw-s o qn 66 s. The stairs 2z3 fos wpxqzn+/-nn+ 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 cycl(gj8qonj zma-,0/4p0 ha ex) xi)w*ax7daz xfist 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 maximum power output of 120 hp. How steep a hf:crl 3 o4m,mt iyq;;0nh *vthill can it climtyvn0:q4lf,o* hm;t r i3mch;b at a constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box ch *njro3v -bjx95-wkalong a level floor at a speed of 1.cko-vbw 93x5jj*-n r h2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0k l ,pxq1y+8dhy*e n2e av*6ul $^{\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 buzo m3 t0.8/jijxudyry:9h4 b nilt “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 bzjjr 8:it. bd09y4uohnx/3ymumpers 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 the ground, and ( ,xy26 kl 8 itwzbxo7ci6aaxr) a8ea-the remaining four shelves are each spaced 30.0 cm above the previous one. If the average boobarexwti( ocxxy6a6ia k)a , 88 -2l7zk has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics sh o;nbgcxg/ct03 9ber 0ows 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 lgcbtb9 engx ;c or030/aunch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without fd/q49 s nz ebcg9jw9+yriction 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 loop o9/9 g9cb qdsz wyj4en+f radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraftr .7www5d) deb without his parachute opening. He landed in a snowbank, creating a crater 1.1 m .rb7e www5d)ddeep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L who /* smd(yn8doi)yf- o-t8nyflse other end is fixed (Fiyl-8o 8fo ndy/)*-in stfdym( g. 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 the top of a 3700-m-high mountain. The climb is)u sz82ih .;7 ggfbnwg made in 5.0 h starting at anwh zu)g.2 i8gb;snfg7 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 breakswt8 .xi+2hm dn 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 c8u b bhv)k8dsa )8)rma,x2 gjclaims that its lifts can move 47,000 people per hour. If the average lift,)8)gu av8da)kbh8c m jr2sxb carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m n.5lyb.h mjgzle+0 b+ before striking the turbine blades. Calculh0 ge .b.mlj5y l++nbzate
(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. 6–44), the /uo4e( d.+ai 8acxreddifference in your apparent weight at the t.ddo/x eu ei 8c+ra(4aop of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly intslst0p iw 9s ,d2-bi6 ;uor6jpo work, how high could an 82-kg man climb a ladder 9p,sjr -l2uipo sd6wsi;0b6 t 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+*l: 2fq5pmxi vy*n zp.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, thej+ue8l u (s4i 0w90oxtpa;jdz /9u*oth.mtpy spring inside the scale compresses 0.60 mm, and it tells you your weight im4p+9ljiuzyd o t ow sp(.0/t 9jut0;8uheax*s 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/s3r*jpuqt-y vd(*z 3p4pscx2q nx+m9e grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is zero. y9vxstr m*+zq p2xpc d- n4 pj(3uqe3*
(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 4, gpdgqhzhi m*z5j-so.lw885q6erp 8me 9va vertical distance of 5.0 m in 9.0 s. What minimum power output wvz8qdre e8h gi*,wzj86 sma pm.qhpg4l-5 o95 as used to accomplish this feat?    W

  Some electric-power companies use water to store ener6m k bum.:0wf/xpyb5/as .gqtvg. p*b gy. Water is pumped by reversible turbine pumps from a low to a high reservoir. :g0m/. fybq*kx av.bw.mg ps6b 5tup/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 7h .xwc3 xgj5wog39lt. What is the spring stiffness constant for each of the two res373jcwx 59xhgo gwl.tulting springs?   k

  A 6.0-kg block is pushed 8.0 mhthco xv .nc 39;dj 4kp4b*)8cfl 9nmk 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 35e, z8ful8mo;.p:nffq km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays tff, mnzleoq. pu:8 f;8he same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks o,ch-a9+qh k rpn an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadm -ca+hh9,qp rkill 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 upward a distance of 500 m, wh4vw9-+ lz:5 t cuzkvkpat was+wvzc5 v- klpuz49 kt: 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)ck5o(vy psi/;u8 0 1ttyu2swv If this water wheel is set up to provide electricity output, what is its maximum power output? t kt8oyiwv5 s;1cp0 /s(2y uvu   W
(b) What is the speed of the water as it hits the wheel?    m/s