In what ways is the word “work” as usej81;it jpq5e.glz t 8:nyy*nad in everyday language the same as that defined in physics? In what ways is it different? Give e 1a z* tq8:8.n yyg5iletnjjp;xamples of both.

Can a centripetal fortz-1fji3k ;h nb(lc)). tixbrce ever do work on an object? Explain.

Can the normal force on an object ever do work? Ex0n g*q)asz g:at4tx ,aplain.

A woman swimming upstrg/, hn1c 6)whdgbz x-leam is not moving with respect to the shore. Is she doing any work? If she stops swimming anl , /6gdn)zhhb-c1xwg d merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint:x 6clgm4n3* p. uqpqp9hmvvrw-g5 -kzs z-32q Consider what happens to the dishes when you pull a tablecloth *6235-nzm p 9x-4cp r v-pskvgq3 gwlzqmqh. uout from under them.]

Why is it tiring to push hard against a s zyoxw21(e27t9vqu vl,v-o 8t3bd swgolid wall even though you are doing no wow3 vztvx1,vdw7 (o2l2tu obye9 8gs- qrk?

You have two springs that are identical except that spring l is stiffer than s(qe3ayxx g /ab :l-8pspring 2 ae:g-qpl /a8ys b3(xx$(k_1>k_2).$ 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 utj9,c:la 97p c4+pgprvn/9anfw) i ca block that is free to slide on a frictionless surface (Fig.6-30). The block starts fromwc 97n,+4p:la /gvnuj )crctp pf9a9i 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 p ;qn t isa4h+k.zbkldbff*7,* otential energy change when you jump a*asd .*iz qb47ntfb k;l ,f+hks high as you can?

In Fig. 6–31, water balloons are tossed from thx2j g0fv q(wyk*h;4anc8j5 gqhc 46fie roof of a building, all with the same speed but with different la2 44 g6qj vjkq8 g(h5xyihwf 0ncac*f;unch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest poin+u)*zvv4h lq kcg869 i blwx0at 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 secon chll z)* 89vk +0viw4uxbqag6d 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 e ;jv4 -jwlo*gz-qp1 zthe spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservago v*qezzw1-j -jpl4 ;tion of energy.

A bowling ball is hung from the ceiling by a stekk7-)ucrddghsocf 38zi.4b l:x 4 0leel 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 instructor is supposed toudd4 lbxs:h r gkz40e iflcc3 k8o7.)- release the ball without pushing it. Why?

What happens to the gravitational potential energy r*9p+h r5f naxwhen water at the top of a wateh+9 5 rnfapx*rrfall falls to the pool below?

Describe the energy tra(q m7d-9 3 voe-zyxddctd0-bxyht, )nnsformations when a child hops around on a pogo stick.

Describe the energy tra4/ph1 2 fev /xenoje,unsformations that take place when a skier starts skiing dow2/x/eopu 4j1f vhe e,nn a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m)-ij r qy3gvm / ivdy1o)*u)lf2 starts from 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 friction, and (b) there is yd1 vjfy2vm o)*qlgi-/u i) r3friction (deep snow)?

Seasoned hikers prefer to step over a fallen log0n6yf kjn 5b.x/2tuib7i c:sx in their path rather than stepping on top and jumping dof6t :xi 5i /uybbnjc7s20xk.nwn on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired )e-mlsdip 0e7/. nhft into a bale of hay /-ndpt0. smle7ef )ih. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a si1bmh 4:/tb ij;)itz-taecan + mple swinging pendulum in terms of energy, (a) ignoring h1t+i;j: b-nz)eamci a/ 4 tbtfriction, 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 hn0leye-i0 t q;eight greater than its original 0-ei qytn0e;lheight? Explain.

Suppose you lift a suitcase from the floor to a table. The w8wemo xa zo/ +wuu*yz:d99l8xs :8r leork you do on the 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, (c) the height of the table, and (d) the weight of the suitcas/u 8xluzw *98 o leyawsdz:m: +er98xoe?

Repeat Question 22 for the power needgix38 obmn :vg++dgz/ed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb s zhk+4 kf.qmvz8 8qcg/o o:ki/traight up?8f.v z4khcgm:+ /kk8 iqo z/qo

Recall from Chapter 4, Example 4–14, that you can use ,k1ij (a93w)vj7afbayp( bp t a pulley and ropes to decrease the forap9 a p)1ajb(ij(w 3 fty,7bkvce needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational fw-: vz )4dchdhapnm;w 85ac9 vorce when a 265-kg pile driver falls 2.80 m? pc9cn w- h)a4v:;8z5dmvwhad    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m h x+t2u(74- *uk dwyihre2ylvv;vl h;90 micnxigh. How much work is requih +rd2m*4lvte7ulywxk -x h vu;iy0;(i9v2 ncred?    J

  A 1300-N crate rests on ta(1i tia s*p)zum:4xkhe floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction forc is4 tx)(: imazup*ak1e of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work di9dzxv c20 n:ntd(5 quqd the movers do (horizontally) pushing a 160-kg crate 10.3 m :2d5xnq0vd9zt(nu cq across a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleg,(upx d);nx ma2)mucrated by a force across a floor at a rate of for 7.0 s. Find the net workmduxa)2u(;g px) ,nmc done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a tablefhbc(s/9 m /v(wth ey*. How much work is required to stack them one msycb(/* /t(evhf9hw on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff gz rqv 66.-6ywvp(gihobjects we might not otherwise be able to liff. Show that the ratio of outpuggpzv w(.6-y6 hq6vri t 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 down0i0697cgyg3i1+ he 7(o n eno yuzsdon a 28° incline and 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 is 0.40. Calhoy 3on7oe1nuc gy9 densi070( i6 zg+culate:
(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 requir-9w6 ,:pdt sk(unr yj*.f6 gosjcxq:: 6 rgoahed to give a helicopter of mass M an acceleration of 0.10p*oogj 9:n kj6(-6af:qg,scrw uh tyrx.s d: 6 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 gy05n 9o(:tae qyt7aqzz. hr-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 axis,xd, f+hsj+a4 chfm/ .yf-7w.eckrm; q varies as shown in Fig. 6–37. Determine the work done by this force to move t+,c ;qfh+fd4er.-/ 7mxjmhsy .fk wcahe 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 p * 1dqqqb2/ejlyq -zab0 w;d74b7cb saarticle 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 p2gb mxpe6) ,hrt7ou*: lddz;oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what fvc;ebj ; hv4w*r9v2:jb wakq,actor 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 stohyav6e0mcp 4, p 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-k+tm n bjmr+k3 a8z:zd*gcar 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 af6g fa(m-tidrvv 1irz:0 );wnverage force of 110 N on the arrow over a distance of 78 cm. What zf)da wn6(vi g ;0i:m f1r-trvis the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) trlnum *x)x+ u/laveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball)/+*lnxxu m lu on the glove?    N

If the speed of a car is increased by 52 q09 zsdagt27onw4)uv yq0- n;jnha d0%, by what factor will its minimum braking distance be inc2awynv9qh 0 od 0sdz-) njt2u7gaq4;n reased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a levehyn7o)o4v9pj+f 5xocl road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and thjv4p7o 9noc+ oh5 )xfye 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 s)f;9,zbt a no0.25 kg 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 pitch, if the distance betw ntos;z9 ),afbeen the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go ifr)dl8.ys0+ f;cjp.o g /yds xx thrown straight up by someone who does 80.0 J of work onj0 xfgr.cx s;dy8lyd)/+sp .o it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration 9tn7n 5w 2ne gqm9gdi0 by a single cable. Determine dqwmin7 5ngnt9920ge
(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 mhfajpu fby0 *b .v10v0;fmmv 7uch must this spring be stretched to store 25 J of potential enervvbp 0;a u fv* 7fyj0hbm0fm1.gy?    m

  A 7.0-kg monkey swings omnc (gx(-s2lfrom one branch to another 1.2 m higher. What is the change in potential energy (sgl-2onc(mx?    J

  By how much does the gravibhoz2i zk p5ae4(7 5uhtational potential energy of a 64-kg pole vaulter change if his center of mass rispo kh 4257z eiazh5(ubes about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kp cegely0t)e +t, 4/qll s:o1km/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 of the spriglsp+etc,4etly /kel0q)1 o:ng?    N/m

  A 1.60-m tall person lifts a 2.10-kjsd*u0f ;ts6dg book from the ground so it is 2.20 m above the ground. What is tud6s djs tf*0;he 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 and climbsi-nu 5e-x ty55e,njyf4 ne8e g to the top of a 3300-m-t e,xe5g8nnj4eie -nfy5u 5 y peak.
(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 7.ggsf yijj/a4 3-znm 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 7gzyais3. 4fm n/-gjj up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top s3 /9 czr+zrpein l;x5bpeed (5.3m/s) and grabs a vine hanging vertically fromp59 nbr; / rzexci+lz3 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 frictionlesszs+fs:;kji)1e fq62 fy hrj o3 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 frictt +l*vtf7 y,bdziwxay3;(q( xionless 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 gravitatiy..u7n -ibnsxonal potential energy without the aid of a pole. With what minimum speed musn-7syi u.x nb.t Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artisttg0 tma r ex1kr/h,1f1 jumps vertically upward from the top of a platform with1eht 01 k1/rmg f,raxt 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 stifs;5il2m mli p-j e23iyue/6 zufness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What ume6 mep/iljz-2sy 5u2u ;3ilipward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along i.fnlpdd0n*v -px .z3the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (p.3nf*d0l ivzn.-dx p whose radius is r), from what minimum height h must it be released?    r

A block of mass m is 7x 6ipy;ve59s s5bo;v hsv/ud attached to the end of a spring (spring stiffness constant k), Fig. 6–40. xyve 96 v;bu5 5iv ;hspd7/ossThe 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 ekr 9)ngbl9d+p7z .f2 pn1wip)mh4bm bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law ap2 .i kbhpd1+b9fml7r4nngemw)9pz ) pplies. $\approx$    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 t )ru:4,g8ovacmsc7r jo point 1 where it is released from rest. Assuming no friction, calculate the spevcm ou 8cg4rsrj,)a :7ed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with ad 84yhxis4s6n(7acuvhf0 u,r speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to +klf. -9lxcb qbe placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more t.lkb l9 -qxcf+han 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle u a4+no. /z5 tszikbv0pp 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 a pgpz,id,2qj 4nd traveling 95km/h in opposite directions, collide head-24z gpdij q,,pon and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descenw;b5df( ;o/ l g6 xn3s pgxw:2uj6pznil)j,svds a slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this process? 6z x ,xufv sgbwd(;2) j niln3ows;p/j:6p5lg   J

  A ski starts from rest and slides downnnq6k knjd: r/+w)h l6 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 a 3 moiat:,z8 lkzhu f7nvc idho4z1719bove the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.5 psedl +wbs, )0msde +p0)sl, bw.
(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 fromjnh:xzk2 *ds2j;el z. 1 i.ltv rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction lne:jjvl *z1k.s.tx2 dhi;z2 is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pasz99tm*yk3gt k-c2 qr nses point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distant 29-3z9 kyrn*cqk mgtce traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of dzz)xd +8vqzgb2p:) j 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 att.v2f87pyyxr a9tp ,pyached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is ,fxv87a tyy9r p2yp.p noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attachedkx4w/6mkgj7z 2zukd / to a very light horizontal spring, Fig. 6–40. The block c 6wjm4/g /kz27kukdxz an 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 position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle usedmu1 tz4+ 7n:bqnv t)jagh6aat(ayl/: a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventuallyn6l:aya)tztjhb+ v(tgqa nu1a :m 74 / 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-W motor to lif mv2 a-y4y8hsp-bscbt iwd/tj+ aj6-(t a 315-kg piano to a sixth-story window 16.0 mjv/p6bct --i(y42saa sjt8+y d-b mhw above?    s

  If a car generates 18 hp when traveling at, u0o8uqzy00s db2 wyw a steady 88km/h what must be the average force exerted on the car due to friction and air resistanceow uwqy20zbus 8y,0 d0?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What ik7ipre5 z3vj77 idw7z pow80swm:(m us the average power delivered s pz 7ri3m5:7w8 dkiew0( jv7u7pmzowby the engine?$\approx$    hp

  (a) Show that one British horsepuu2trx w72f4v 0s ;pgsower$ \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.rzxig9 q crw7gx9 533r”
(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 slows0ed0by;us :rzpy3s:fo((h y i down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (:yz(yi(o3pseb yur ;s0hfd0:watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.06h 9ux9os 7 +iq0o(pjjzp0mkm-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.: t czhsor:+9p3-kg shot from rest to 14m/s If this motion takes 1.5 s,cotp shz9: +r: what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per m:xxs9 qp n a 40sklgyvbb24r.5inute through a height of 3.60 m. What output rating (watts) should thrsp 42bq9v:s 5.yxx40 lnag bke pump motor have?    W

  During a workout, the football players at State U. ran u saln*o 4vn)5lp the stadium stairs in 66 s. The stairs are 140 m long and inclined at an ang*l5a)4s nv lonle 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 climb 7wcil*5xabri( 1 e0hy 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 hill s2(fflbn)zi yyfvb .:;2we c*can it climb at a constant speed of 75km/h if the frictional forces add u yfn s2(2b. lw*fc :fvi);zbyep to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box alodv(gilu h :g:(ng a level floor at a speed of 1.2m/s if thg v(hgid:u:l( e coefficient of friction is 0.45?    hp

  A bicyclist coasts down wr(:,np caqdib0um. .a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8kmsoiyc ea7/js80 zo w66/h) bumpers” that are designed to compress and rebound o66zy8j0 ciseso/ wa 7elastically 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 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 c 76z-vsl6 zynzi8j4fkm 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 an68vl kziz jz7f- ny64s 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 yyugrf6,n de fq1.h6 /jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he w,e6yr y/q.u6d f1 gnfhas traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without frictik/(a kc,(w 2v us/vu6 ol5o7sgtfpb0qon along the looped track shown in Fig. 6–39 is to remain on the trat(2agukub,s 6v/cl5q /(wpo f 7os 0kvck at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from a up .z t c/vdlow9/*r -jyvg6(oet5r25 zvhr7on aircraft without his parachute opening. He landed in a snowbank, creating a crater 1o ./ rh*t-jyu ovr7/v2z5pcg(w5l rte 6 o9dvz.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 of length L whose other end is fixed (Fi(c-dr1ql3o/,t2e ong bq ps:mg,d ot/cb: psm(enr2 og 1qq-3l. 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 clim 55argeordz3 kcl, d87b is made in 5.0 h starting at an elevation of 2300 z8,ald r53ocg75de rk 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 abov,b)v j1mzl4c9 3 knuyq5kvmo+e 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 Califb8: z +ywo+ovlornia claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, vlwoo8 y++:zbestimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam p76 2ev;r zg2q5upy)b zgw*sbjqcq/ 2at the rate of 650kg/s and falls vertically 81 m before striking the t) g2q j625qp7*vcre guy;p/2qb bzzws urbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coato, n6f);ymx 6-oc;u rgj;vguster 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 also that as long as your speed is above the minimum needed, this answer doesn’t depend ;,o6o;; xftjv g uym6r-u)cngon the size of the loop or how fast you go through it.    mg

  (a) If the human body coarur g.afg 1 n 90xh,yi3tm;2ruld convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (rtg,0g 39afi 2rax y;r h1.num=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 4n7u gm+f6 ay gd;o*pg45.0$^{\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 insidesqu,.6bxrt jh8lr fs9 *w1i3 p the scale compresses 0.60 mm, and it tells you your weight is 710 Np. h*sjxr bwf63 i9,ru1s lqt8. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings z9v v4nx bwonr2cg-22out over a lake (Fig. 6–45). He releases the rope when his c x nnrbw2v-9vz2og2 4velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m iny0)j zsdhwjn0 meiif z5. 2/(k 9.0 s. Wha0ws kjy.iz h/(en fz0m)di52 jt minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store ener g3kpz3tbo h)+leha8ij z(; 3rgy. Water is pumped by reversi8 k3z3 prei;)bhl(jgaoz3 +t hble turbine 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 is the sprinwiua 30c*1 fjsg stiffness constant for 3i faj1*cus0w each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough dyn3d xccbr*m(0 mo4o v n44g837 $^{\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 frouk u8zmg/)c;fj t01p e3*mxrym 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 7j1xetr* kpu3) 0cumf/ 8;zymg5km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac funnw7t ,ajv2c k;ction (the “stress test”), the patient walks on an nat7,j2vcw;k inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a dist .:z .visrx;0asjy ib86wuzs * p-j3wxance of 500 m, what was its velocity when it left the volcano? r 8;jsvxbz ..siyj:x6zw03 apwuis-* $\approx$    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 heig3wh+bkd jn4e7ht of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum pow j+n7wdhk4be 3er output?    W
(b) What is the speed of the water as it hits the wheel?    m/s