In what ways is the word “work” as used in everyday.3f;d7 fp-. azux tazc language the same as that defined in physics? If-a;puz.f7xct a.3zd n what ways is it different? Give examples of both.

Can a centripetal force ev6s6 /uks5pmu -x1) f eggt0lixer do work on an object? Explain.

Can the normal force on an object ever do work? Expl bfs;30i yr,m*wdvw( cain.

A woman swimming upstream is not moving with r*bgz- ws1n)ojpexdc;l e j35dp4i-9mespect to the shore. Is she doing any work? If she stops swimming and merezndbo 4)dp3j-xls iwe1m; *5c pjg 9-ely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hiirun.zbe (h -iy-. *a*zh b2pc*pyr o3nt: Consider what happcip r3-*.z(*py*2bz.ihr any-boeh uens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even .rick7a-ua8b+ 4ouo/ ;, jo7unkscnjthough you are doing no workr8jnaauo o;- n7 .4u,b j/oc+ skui7kc?

You have two springs that are identicalii1jc( sa9pu0o**s sz6 l6q jx except that spring l is stiffer than spring j0q6 p xuji9sli*(*c61 soz as2 $(k_1>k_2).$ 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 to saa (4oa)s qw/.u8+rpi 3rcgmjo.j5rtlide on a frictionless surface (Fig.6arrq5tw 8.4 jiu (jg3ac.+ mrpo)/as o-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change 7) d3zb6ahcld when you jump as high as yo3zbhd7d)6 lc au can?

In Fig. 6–31, water +wn rpye.mz)vy b 0(5cballoons are tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed ncvw+r0 ).m be(5pyyzon impact? Ignore air resistance.

A pendulum is launched fromp4 28wj7 ztsxg a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an 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 eq xwztp gs8j472uilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compre3 :vgjk 48yt4r m; 2aqtje/wth9e wk e+je(:buss the spring by pressing down with your hand and then rele(k4: /gvj 8;jb: e9k wyw3jtauqmre+te e h24tase it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a g+ eo e-yh98zqsteel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the -e9+o8h qzeyg instructor is supposed to release the ball without pushing it. Why?

What happens to the go,6azu fn q88pravitational potential energy when water at the top of a waterfall falls to theopu z8f6q8a, n pool below?

Describe the energy transformations when a chili;f frbx m4 -(jt1gn1jd hops around on a pogo stick.

Describe the energy transfoges:vmo*( 8kx rmations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a*8m(k:s gev xo snowdrift.

A child on a sled (total mass m) starts frz 5,fjx5 hts00bhvh7/wp :fdrom rest at the 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 frictionfpb,j0w fhr5x vt :hs05h/7d z, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather th9gk1 pucpx ibjo; r7:yjjir8f0i6( y gx;k0 1lan steppinl;j(1b08o ipfk;:y yr79i j 10gir6gucxxkp j g on top and jumping down on the other side. Explain.

Two identical arrows, one with twice 9xg cz16n1hne vwk1t7the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fas1 9hc1wvgxez7nt1k n 6ter arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) igno z.06xhkp ifl;rw; ydf47cr 2cring friction, and (b) taking friction into account. rhdf; 2ip.;yk4w06lrcfz7xc Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height gre+3l 0 ws f psb+e+sk(jv7;tqzm )0wrsqater than its original heigh3ljrmv0s( +z qw p )sf+kse7s+ 0qbw;tt? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on ,reeu(2jgvnbnt* - )fthe suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, bnv*f ern(,tuge)-2 j (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rathet8(7fz:bmoagyk d ;k(r than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb/flfuuxvvs1 5w6:ss4 straight uu s5/1uw46vxlfvs s:fp?

Recall from Chapter 4, Example 4–14, t b;bpf38sqd7 phat you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). Bu dpb3 sqpf78;bt 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 265-kg pile dr md3q,;g, k ii8w6jy-ecwkfc,iver falls 2i,6, cyjcf wi ;e-38kwkgq ,md.80 m?    J

  A 65.0-kg firefighter climbs a flight o .*hkbhqj*j3 m0cjrlna/4erl j /wk,;f stairs 20.0 m high. How much work is requirjqhl *whj , k/l0arjk3c/bjmr. 4*ne;ed?    J

  A 1300-N crate rests on the floor. m 1m*8*y wj*h s b.7hd7menwyaHow much work is required to move it at constant speed (a) 4.0 m along the fn*h.wmd1y7 mwb8mhae j * y*s7loor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushius): nq2mn5kp9br dh,ng a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coe5hq)nrd ks2:ub mnp,9fficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a o7af 89lle,yqt:ac 1urate of for 7.0 s. F8e9u,layqt1c: o f7a lind the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Howz-b bi+q : ydc3hto..w much work - dczy.btqo:h. 3bw i+is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we migg kymzg6(3ps0kah y.fj,o 8 jbrfb-iad52 :x,ht not otherwise be able to liff. Show that the ratio of output f5,zpm gjy -: rkfigfhk3ays8 abo(0b6j .x2,dorce, $F_{\mathrm{O}}$, 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 ,ti: z+ji wavf53m6n4d) ijf s5vuf(b from accelerating by t j mfdj 5s 54vi n)iua3v,6:+ifz(fbwa man who is pushing 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 helicopter of mass M an2bze o2 8ro+s 1z;)biyckzh f0 acceleration of 0.1 i0h2zrbez2);b+cos8zo1 fy k0 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis hyng9d:fb 2 -ais 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 axis, varies as shoij mdeq +v:q84 zk0h;twn in Fig. 6–37. Determine the work done by thi qdj4z;qihvm08t:e +ks force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts in t)u 8u4 w0up4a7ybgo1y) b okgehe $+x$ 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 magu8v-wpa g7 bf+nwj ( ;m5so;rss of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what facf9/a bj atv3m01 nh-wjtor 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 sto0z 4wbp6(nywd7 0uhh(b n3 lctp an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling rz.:i db8w0ch at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exn g0j2w;g1 z7o n1ns5e1uaweterts an average force of 110 N on the a25ns1g10e1n7; ouwtegjwa n zrrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove bn pe/vef- isbp9 zw:kq)/e+7vackward 25 cm when the ball is cau +/7wb-pzv v kese)/9p ief:qnght. What was the average force exerted by the ball on the glove?    N

If the speed of a car is rx/ y,xqce ,d8increased by 50%, by what factor will its minimum braking distancc y xd,/xq8re,e be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a c4j-xi*xjk7 cu 5gm .oyar’s skid mark to be 88 m long. The accidm x*ji. o4-cykxg7j5u ent occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it rew-- gh3ym)j1ssbz,b03f m e5(mmgd5or1 hahhaches the plate, it may have slowed by 10%. Neglecting gravity,g,3m)md0m hzof gmseh sa1 5r-3y (jb-1 5whbh 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 govf4x*ub -c98xl5 wofm if thrown straight up by someone who does 80.0 J of work on fxx- *vo fwl95 4cmub8it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically )c1) bkwz5ujh with an acceleration by a single cable. Determine z1kb5 u)h)jwc
(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 much must t5fb :-+wubvs frla-e/his spring be stretched to store 25 J of po+u- -bvw5s:efbflar / tential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.ngmdn7gvi7.*1 p( rgn2 m higher. What is the change in pot .vni drmn npg(7*1g7gential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter )*+gayrk1k yk1ey p(m;e ;cvnchange if his center of mass rises about 4.0 )yykp 1a1nyvk ee(*kg+m;cr; m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kmz k pkrly0b4-oo;o n3-/h when it strikes a horizontal coiled -k-po3o4l0 nk;zy ro bspring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20c/b*f+ dpdv+kd4n r2o mn2z6w m above tf2dcd6r +w* m4b+v nd/knz2pohe ground. 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 elevation of 1600 m -x p0dhkflf (z2.x )cyand climbs to the top of a 3300-m peak. 2dz(-k0xh.fflycx)p
(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 verjl udd46ri2 ur*icl w.l+m6n( tically 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 wir6*jduic6im (+w .rl 4lndl2ull the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan,pcusqs1i3 t48 is running at top speed (5.3m/s) and grabs a vine hangq 4i1 ct8psus3ing vertically 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 b c//s 2ll8zewfrictionless 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 uky4. smi.f7dxl j dq0,s7yo7a shove 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 kinep32*ar5y ;x msb iw+ebtic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran les5 ix*3r;eamb+b w2y pave 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 up9f k javrjpv8x)y+i :jr. *+8vanp e)jward from the top of a platform wit*y rvx8) jfn .pk8 :aivjr +jja+v)9peh a speed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness constant is 950N/9:py je jdl rtbe27 fe4/m*p/3lcsbq*v5weg9 m is attached to a table and is compressed down 0.150 m. (a) What upward speellg jc/* 99mj/7rd:5 f ebepv4 esw*p2ybq3e td can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides bu9 c9k pfj.c58s, b6spv3jht without friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released? pc5hc9.3vss8kbbjt 9pfu6j ,   r

A block of mass m is attached to the end of a spring ( y u-m;y8k5e(6o )aza8 lpbfjgspring stiffness constant k), Fig. 6–40. The block is given an initial displacement ;(pj5ue)gk m-8 az yb6yoalf8$x_0$ 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 i9)tvj6 b l/mkcq2b0wcs tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k lqj k w96c2b0/b mt)cvof 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 dxo,m-8i8tzj6ee pwi6 ragged up to point 1 where it is released from rest. Assuming no friction, ca-8imw 6 z8,etixje6polculate 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/72 hbd4zcq0xa o*qf 0ottw:0i 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 desig(c bec 5djnf yi4zkw3,;cbl4:ning a spring to be placed at the bottom of an elevator shaft. If tcc y3 flz;44wdbk:5jinb( , cehe 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 passengers.

  A cyclist intends to cycle up a 7.8 zfrle2 bm59 ax2q .xr+8bkbs 0$^{\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 95kjyhkv2a5e/ ,um/h in opposite directions, collide head-on and come to rest. How mu5u v/y,kjha e2ch thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descd lmqc;, . .a x(d5s)gudln+wqends a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How d5 )s;lqdq,+adw..mg(u x lnc much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides k+)xv cjp(wy *gczu(;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 t-0/yze5 / rph h1vgfvmhe 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 baclh:jw3y+7r7b*z dn 7s *bzozok to a height of 1.5 m. 7 7o3*wh* bojzbz:nzlr+7ys d
(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 conw4hr 2m;r zn1. l mm1qo/rpdrea j gg,n72q)i4stant 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 finaz, rgloh4;rw1mgq.aidem7j p qm2/21) nn4rrl speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes pointl45f rw-*+s e. jedgrt 1 with a speed of If the average force of friction is equal to j-e*.ew+sr f 5dgt4l rone-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 reaches the foot ofyr rzhgezb 7o k;-j390 uf:t0k a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (k=1s2rm 6 r8jso.6psffjnzc )u7+80N/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 beo8. )6fu ms 6+jczn2fjsr spr7fore 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 springapkre:zyt r; ;:uce u/a7wh.g 4y. h1f, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this posit;4;uft.zuha ew:7k.arphey/c1 y rg:ion, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttl 2pr: 8whoy(/d(-yfvsk,(zy(pkfw h ye used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from:w ydp(fy28kfwvh(,-rsoz k y/yh(p( a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-ueyv -+ 5g6z0unrb18pofwy w7 W motor to lift a 315-kg piano to a sixth-story window 16.0f5eyzwg 1ow 6+pvy-7b80nu ru m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the xkdkeq6m;85hs)rue8n /-fi raverage force exerted on the car duk x-m85u e;rqn skr)di h8ef6/e to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the a- e.xy,mg oxjp)u4c2tr5wm5 average power delivered r,ymm5g4.x5oa xpu )e2jwc t-by the engine?$\approx$    hp

  (a) Show that one Bry,(9 9 dy+qqi5 y,hy9xf fubogitish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowatt-hours.)6tqt e/8oims”
(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 togj9ibv q.0 n9 -eimk e)iy-9lj 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the cae gmy)q vb9jilk-9.ine i-j09r traveling at a constant 75km/h.    hp

  How much work can a 3.0- az) hc+15 c5-e8aeu njf7luwihp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from restm0)xj l9ln y+j to 14m/s If this motion takes 1.5 s, xnmj+)yl0l9 j what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg ofsjg /+9iqu+ecsxa/ 6 ch t+wi) water per minute through a height of 3.60 m. What output rating (watts) should the pu+c9c +hsgq+xe)/ wju6sa /i timp motor have?    W

  During a workout, th+5m) 2uu*h5bwnxrpvr/dyw kk u* ia14e football players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m iwv *5up+ywd4kr21unbr )*m5/kxuh a 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 cyclist x b*ecfo:xbap4 5zj* l4 -p6-b magiq,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 steep3;+b vp56 a pkfqyko4g a hill can it climb at a constant speed of 75km/h if the frictional forces a pqp3;bg+4y f5k6 kavodd up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor -ppwp,, es gp*o+jkb9have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coeffici pep9k- +wo b,jpgp,*sent of friction is 0.45?    hp

  A bicyclist coasts down age7h9 h/ugmhaz./, en *8mb fp 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are nu *:rl.nb ux;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 bumper be, assuming the car has a mass of 1300 kg andnnuul.* b; :xr is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0i gmwr.b2 ;kyv/j8 b,d 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 shelf holds 25 books,dk.; 2jwygbb m8/vir , 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 s481 uqrs,)/ oe jt gfpvjln44b.v6t buhows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he /s quotf)8ruvv p6n1l,4bjj.t bg4e4 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 9/gchhoh jw/- looped track shown in Fig. 6–39 is to remain on the trackh- /ohh /jwc9g at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m afte-ig7imu6w:0e32f4s vkjmf d lr jumping from an aircraft without his parachute opening. He landed in a snowbank, creating f3j 62smf0w4el7g k ivi-u md: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 ofs2qgp- o( uv0w length L whose other end is fixed (Fig. 6–40guwqop v2-(s 3).
(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 t2.8gc 7pi qnt.gif l.vo the top of a 3700-m-high mountain. The climb is made in 5.0 h stlvg gqp 8.tif.n.ic72arting 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 ic8yz-(ipz u/i s 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,2pt1dia,5o t w000 people per hour. If the average lift carries people about 200 m (vertically) higher,1o2 ptt, d5wai estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls v+lixh.:r z*rvertically 81 m before striking the turbine blades. Ci* hxzr:rl.v+alculate
(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), od pil5r9;2hm +*x agfthe 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 also that as long as your speed is above the minimum needed, this answeropxfld9a g*hr+2i5;m doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could converto ,( bu9ej,rfl a candy bar directly into work, how high could an 82-kg man climb a ladder ie(fuj 9,brl, of 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 a)ltb,o r0 xua1x/2 j b mw8rxuo*e,w0dt 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 scale compresse 4m cq6i,hii,gs 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1 6i,4icmgh qi,.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs ;c(h*ei0h8fypu1gi fc 9 dqz1 a rope, and swings out over a lake (Fig. 6–45).fz*iquhyc;9 0dhe1 ( 1icg8pf 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 1leuo8o01gs eg2 (isxa vertical distance of 5.0 m in 9.0 s. What minimum power output was8 soge 1se 0gl2(1ouxi used to accomplish this feat?    W

  Some electric-power companies use water to store en r3jut e54jp)m99n ytrergy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.n9jj5 m34 trpre9u)yt0 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 sty ;hrgn/ s5e6oj;p;, 6j cdgitiffness constant k is cut in half. What is the spring stiffness constant for each of the two resulting sp y;d5 6h6jejtgs o,i/ng rc;p;rings?   k

  A 6.0-kg block is pushed 8.0 m up a5lj5ei4s nod 2 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 ( .i8t-zg pr pap-c ou00e5umgs, how long will it take to accelerate from pmu gac-8egr-0zo5uip0( t. p55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac funmy* f2 c.rxa9; mapze,ction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patix9 2a,re. mpymzac f;*ent 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( vwtf/ktxnxi )4c j3o8j rjm4tdb72. -kg rock vertically upward a distance of 500 m, what was its velocity when it left the volcanoxtic4d4t. w)m2 nk/rbjv ( 3ftjj7x8o ? $\approx$    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 l v-ogzky,:.bheight of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, w-gl. b:k y,zvohat is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s