In what ways is the word “work” as used in evdijm.ip)z yxmy; +d h-rge1g6+ g)-j ceryday language the same as that defined in physics? In what ways is it diffexze 6yi+1 -)dr ig)hc gm ;.jgpmyj+d-rent? Give examples of both.

Can a centripetal force ze fa2r + d:oln)enu/*ever do work on an object? Explain.

Can the normal force on an object e.5zrxckp 8t/(tr8nk epvk; uri01 z1m ver do work? Explain.

A woman swimming upstream is not moving with respect to thgspyfz hard4bt1 0 .3fgnq :/(e shore. Is she doing any work? If she stops swimming and merely floats, is work done on h(dy.:a/sfnr g1qtp0fb 3g4hz er?

Is the work done by kinetic friction forces alwaxw+y) xq3s)quys negative? [Hint: Consider what happens txqsu)+x qwy)3 o the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wals3 7qr.m:;i*-bdv4twjvw mkg l even though you are doing no wot*kv4 v 3ig:wj-;7wr q bsm.dmrk?

You have two springs that are identical except that spkg62- +t odnotring l is stiffer than spri62tn -+dootgkng 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free,ny vc2w lc*yo/33s5sl2avak to slide on a frictionless surface (Fig.6-30). The block starts from yal3, w2c s/o2kv5cnyal 3vs *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 youjyo4 6s l) obnh*.jre9r gravitational potential energy change when you jum ors4*h) jl .y96jobnep as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, alzy y,8*n.c /kwl1vvh ll with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resinvzlkl/wyc*8y 1, .hvstance.

A pendulum is launched from a point that is a height h above its lowestfheg2 neckh80;jk6a , 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 initikf,a8he6;2 k0nj cehgal 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 upright on a table. If you compress the spring b.pau1vlc / f6kf-z+dky pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation o c 1k/6pvf-+k.ud zaflf energy.

A bowling ball is hung from the ceiling by a sts. gyu+h:m qspzit0 j99w21m1ioab,ieel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid iqyzo9igp.b 9i 1st , is0 +2wa:hum1mjnjury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravi4des by) jvbai *rg7)2tational potential energy when water at the top of a waterfall falls to the )7g2ard)4*yve bs ib jpool below?

Describe the energy t:ua b d(d:rbe jv-v)4transformations when a child hops around on a pogo stick.

Describe the energy transformati h 7: zukf,19v i :cvqwzqees0au3y:;fons that take place when a skier starts skiing down a hill, but after a time is brought to re:1u:uhq ; sqz0fe a,: ifc9z7vvw ky3est by striking a snowdrift.

A child on a sled (total mass m) starts from p iim :)s+0fl:-ftyms rest at the top of a hill of height h and slides down. Does 0+i:l )s :mifp- tmfsythe 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 1.p9t4n lmqzcin their path rather than stepping on top and ju.qnpzl t14cm 9mping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a ba9:0jgdlsmk6sy bvkdv 1p wnd2d( :37ele of hay. Assuming the hay exerts a constant frictional force on the a s1kewdn md(k9vl6p 2 y0dj:v 73d:gbsrrows, 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) igx-, c- mtcli8),jc3i;gtpzad noring fri3ci;z8c,) ti -,-gcpdx l tjmaction, and (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 than itsqxzyihlvun 5 ..h3hg .s1/nu; original heigh. y5nh;/ .nxsu1q3zuv.hglhit? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do 9stekl: t apuam8-/b3( eus*fq 6k -omon the suitcassfka8u /- eoatlqu m*-m9t3 s:keb( p6e depends on which 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 than ty lqj cbel,9(wh;l;m) he work.

Why is it easier to i+ 6nv- v mbobw:zxb00climb a mountain via a zigzag trail than to climb straight up?xoib nvb0w-+vbm6 0z:

Recall from Chapter 4, Example 4–14, that you can usn 8.nkofq6:vpk d);s se a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raisn.)ks8kqp s;v:dfno6 ed, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is don;8o(ux: o-vbww+c2pjhqq dw 91 de2c ne by the gravitational force when a 265-kg pile driver falls 2.80 m? woqnj c+( pw e8d ;ov9dcx- :22hwbqu1   J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much workzev 4;u0b1m tb is reqbzu1 0emt;v4buired?    J

  A 1300-N crate rests on the floor. How much work is required to move it at const3c nhm9p is2t.ant speed (a) 4.0 m along the floor against a friction forcenthc.2 s3 m9pi of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (h zgubn9s/;x3a.j-f yo esw)2 .ag0q*/kdsc saorizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of f/gq; 9no/.2usagzkdsj-)*fbw s e3xyac .0as riction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a flo qn6 fdj,tdv/+q 6uh ac;:i9rgor at a rate of for 7.0 s. Find the net work done on dnfuqjt irc9v6 /6qga:h d+ ,;the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fbr4+jl/:quz v.i ka4w 3pzofgxs5f58 lat on a table. How much work is required to stack them one on top of a3i sxqw4a/zkzlj b54u: r.5fvo8 f+ gpnother?    J

A lever such as that shown in Fig. 6-35 can be used to 4tmce6vld4 3 xliff objects we might not otherwise be364cvx4m ldet 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 kepa+udf4 9geg(qo hwx:+t from accelerating by a man who is pushine 4q(d 9wax ogu++fgh:g back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helja,wv 8z b*6b(sr)stwicopter of mass M an acceleration of 0.10 g upwa8bb awsv( j*twr,6z) srd.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linear and thdi.* ;+z kal-ykn 5zbnn c/;cyat $d_{\mathrm{A}}=10.0$ 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, actinglp jrg+2kn:;:o q )gcc along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x +kcpn o)r::gg;clj 2q = 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+. kau-y5(cpqdlty n+clp as2;pk s9- acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with y/ e5+x*nzjlbf bp+*82 pj9kncadt s)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 s(j+,ebloy1 k 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 st9e 7y+:rpqi efop 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 -j/ gjyhsrv0h v t+g9+4eei m+stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average forny ;epy9+a aud8t-;a 8kz w7yxce of 110 N on the arrow over a distance of 78 cmazp8y+ ay8dw xk e yu;n-;7a9t. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) tragpnlz+z-:j6 lum 2zy(veling 32m/s moves a fielder’s glove backward 25 cm when the ball is zjn 6z+-lz l:yugp2 m(caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, q,gv-fqo +v+ fby what factor will its minimum braking distanceqq+vf +fv o,-g be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level roain++bzu 3xyl95jxu.ai -5lx h d, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coef+3.uuln5iyx 9x z- 5xja+ hilbficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 k-nz i1 8nkqnwiur )tey *grm4,; jr,)pg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitchnkw;etz48* iur) ,-n m) ,r yrpijqng1, 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 d.wegujl)*:y g5k v,z 80.0 J of work on ke g)*,5 wyd:ju.gvzlit? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with u4.- cun7qste an acceleration by a single cable. Determiq7u4c-t. uens ne
(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 constv apl:;6umytd ls,bxv4fd4 +9ant, k, of 440N/m How much must this spring be stretched to store 25 J of poteny vpam, +u:4l49xbv dt6f ld;stial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.) s wf,ms+gn)h2 m higher. What is the change in potentmfn,hg )+w s)sial energy?    J

  By how much does the gravitationa7p lf8 6qdims.l potential energy of a 64-kg pole vaulter change if his center of mass ris idms7qp.f68l es about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal 99iwi)7 akixf ;*dzbosurface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to i*9wd 9xb; i7a fk)iozrest 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 grounvgxh-j 87d vf.oh-zs/ d so it is 2.20 m above the ground. What is the potenhv-xdz 7hv -j/of s8.gtial 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 eleva j,g6dzlxv8 0ttion of 1600 m and climbs to the top of a 3300-m l6 jt,dvz80xgpeak.
(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 c1d 7ivjqo6 r5next 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 will the end of the spring line up w1 jqvd oc5ri67ith the ruler marks?    cm

  Jane, looking for Tarzan, is running at9ptrj5e x2kh .h,tlhd.)6 e-,cjwhy t top speed (5.3m/s) and grabs a vine hanging vertic.r ,)w t9 6dj,hp-ehe2cht.ltx 5jh ykally from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frimaok, krl0/2(y; k.je)fky 2lkqy) n hctionless 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 fribv3. *uc mh/mxog :*fjctionless 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 kinq;*bm;.cn1yiwf 7*/ les:jh9dwt t koetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her cenw;mce q:tbf klji./ow*9 1; *d hsn7tyter 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 from thr2+j33,mrvfs5 ebcm j+ 9xn.sy4udib e top of a platform with a 3svy b.93 fjdr4b+r ni,sxumcjm2e+5 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 sp*e6 w04bnbel sring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed 6nl*4besw be0can 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 4nx vufl,f-o 8pdzj60 track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle08zf6 vpfo ,xn-lu 4dj (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the,m,z i8;aqfo r end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial disp r8fmo;z aq,,ilacement $x_0$ 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 jumz w,3 -yoxd/kcr o7q+of. 5ilcps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffn d/wc q 7f.ko+y -oxi5r,zocl3ess 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 i*mmfb1g f0xl .t is released from rest. Assuming no fric xmm1 b0lfg*f.tion, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed7 8ch8y8q rfxp 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 sprgr ;wyvn(+nco zk(.f *ing to be placed at the bottom of an elevator shaft. If the elevator cable should break whe.c(+kv nwyn ro*z;f(gn 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 up2ycan eet 0h 5xw-:h6r 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 ae4i 4l9dj s(i pykhre;qj, g6,nd traveling 95km/h in opposite directions, collide head-on and come to rest. p,rj, dsglk4y (6 ehi94jieq;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 m high and reaches the bottom with a spet+9q/uyt1 zsded of 2.2m/s How much thermal energy due to friction wast+q u t9dzy/s1 generated in this process?    J

  A ski starts from rest and slides(r7xo5 b33 dyxw ogkj7 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. 218u tdf ;srx.mow2cw
(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 h4s0urm4sposs w,amy4pt( z)j*;n 9a teight of 1.5 m. 4s*4smmw0yur pns z4,;t j(a9)oa tps
(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 pulled across a floor with a constant 0wdpqlz(t1n;k(9 g zthorizontal force of 350 N. For the first 15 m the fl gzdlk(p;t9(tz qw n01oor 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 slnp9jmnlv,q8 3t 3ml+br y(-int 1 with a speed of If the average force of friction isn3ljltys+v9ml8q 3- r, (bpm n equal to one-fifth of 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 rea6t:z d4fc k,huches 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 c9 5cbgk- vgc(to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the tggc(95 ck-vbcable?   

  A 280-g wood block is firmly attached to a very5a nu*odu; f o dj1p:b)uojx:0 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 au* no:uj1o uxf0);o db:pd5jN compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuag8/)qsw3vn2y c y tsd*7ot e4ttle 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 been in the ab scag) ve/ *y8d74t3ty nwoq2ssence 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:8w,4bc9 bjq(af5.glegq2 i5hvicpj piano to a sixth-story window4,ghbl aj( j5geq.5v92q ibf:8 piccw 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the 85y rh7b1u5:qnpf+ v9ssl v qgaverage force exerted on the car due to friction and air resi7qg9 55qynfsu+shl8r: p1vbvstance?    N

  A 1400-kg sports car accelerates from* tuy;ay0zg5r rest to 95km/h in 7.4 s. What is the average powerytgrzu ya0*5; delivered by the engine?$\approx$    hp

  (a) Show that one British horsephpepp hr; b6 +ibeh7-;ower$ \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 “k5im: +juxll eulhk:o*2hk+ owq3 0wv/ilowatt-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 -r6qyjf(fc o8 76wcg d to 65km/h in about 6.0 s on the level when it is in neutral. Approx68(c7w6drc fq f-yojg imately 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-hlh*w,gjwri00 +6razhjoxc:5p motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a ( jxn kof;kd(,7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was ,xdn;(fkj(o kdeveloped?$\approx$    W

  A pump is to lift 18.0 kg of wat07 +r1lsqx9ebltu 3bner per minute through a height of 3.60 m. What output rating (watts) should the pump motor h7b ben3usx +90q1trll ave?    W

  During a workout, the football players at5.vhb9kvqgj+ cj;geq:d, ne f s4yw;. State U. ran up the stadium stairs in 66 s. The stairs are 140 m long g b;9qwqe.4+gvc,: ykh5s fn dvj;.jeand inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist 9glct5o9xg;u)cg r )w 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 steepkf ijd,(wugi a,j*p .: a hill can it climb at a constant speed of 75km/hka:,(g.j*iw ipdju,f if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must blxw.oi+k;d q87rv3 qa motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s;iq3 o b7w.+r xvkq8ld if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 wcmj ypk,9g(g;rk) a:q+ +syp$^{\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/w9p ki5 )d;epmh) 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 9i ; )m5kdwppethe 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 c8gj b ;ub :(wdy2 pb1uqe;7nlim off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all th y u12p;dbubw7nbj: 8;(q iegle shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s fa7dwcgt st(w*iab0)f )wr u; s5mous 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 0;g( a)c)rwdw s7ib5fttwus*of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the lonx9(qbzhq hko 64-p /ryqgn)4oped track shown in Fig. 6–39 is to remain on the track at all times, even)6xrhn4-zqqnpkgoh 9 yq (b4/ 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 aftezr:7de+ ,lyk pr jumping from an aircraft without his parachute opening. He lande :ez+l ,7pkrdyd in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(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 o a+(aduisx(:xk 2ol): tr 5tghf length L whose other end is fixed (Fig. t2: x+ ahgo(:ai lk5xs d(utr)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 mou u3nw)wvp38 vm,v su+5y nplb/ntain. The climb is made in 8 /,nulp+vvbn3p ww5yms)3uv5.0 h starting at an 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 when a 920-kg elevator is 28 m above a huge sixkeu)5i9o8 53 jcp fee4c6xspring ($k=2.2\times10^{5} \mathrm{N/m}$) 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 Californi3l-u2 n: qp8pg mr,ggy6p;xmoa claims that its lifts can move 47,000 people per hour. If the average liftx-,l3:2r p8 uy ;g6mng pqmgop 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 uwy xlhlu; 4,6and falls vertically 81 m before striking the turbine blades.4hu x6lu wl,;y 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 coastergc 14pv wb: tamgu5)s2 with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show ag4swc) u v:2b5mpg1atlso 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, homsl 9i bh7o3ix.*( ufnw high could an 82-kg man cixh .u*o3 7m 9(blifsnlimb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward ang2d +hrgdr3;fw le 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 t90x: -kwduyjo0bbcn+tij)7 r bn- t g/he scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read atk) nn ri/w- t790y+ -:tcjb0ujgd xbbo its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, andtw *hszsx e;-px((/os z(jb .t swings out over a lake (Fig. 6–45). He releases pz(o-/xst .tw szes*x b h;((jthe 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 72ndzpnaq ;ja8n+7c2/q-kg athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power outp +aq/8nqd 7cnz2ja pn;ut was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is ejrga8n7a:y 6 u8r2zpxmxq .9pumped by reversible tuy8x8gaa.nrez79u26qjr xp m: rbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What isxq, qj7vu)wvpkk81vds*xfa6 o c0 q36 the spring stiffnesqckpvfv0 xa, qx7wv8q 63du 1jos*k6)s constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a1-y uf +-hx(xfamkp.d 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 acc 4dvz2lk pzp6nyg+j58s;g 5br elerate from 35km/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 the same, and neglect86zpb5vgg4p 2kz dl;njy 5rs+ frictional losses.    s

  In a common test for cardiac funcwyh m*v :7gx0 u1.wfn2dpub*mtion (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patie hwvmd*.upgfx2m0n7*1yb :u wnt 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 rock vertically upward a d97sgqrveq ,*nmo 93n eistance of 500 m, what was its velocity when it left the vev,qn9es7mg q r o*9n3olcano? $\approx$    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 wa ,xjfi9m3) as y5-junr g2qkic, 8t,xkter wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity o ,mxfkic jn3tg59s,ir)au y 8,kx2 qj-utput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s