In what ways is the word “work” lns,ut987 qosje,vzq+w z7 ;o as used in everyday language the same as that defined in physics? In what ways is it different? Give examples of bothv;sz,j,eu7osq+z lt qo 8wn 79.

Can a centripetal force ever do work on an object? Explh jo )e:2e5dtlnl;gks19 dn7vain.

Can the normal force on an object ever do work? Explaib n/s( xu5mc-zk1 s(np8 zasc6n.

A woman swimming upstream ism mww)h6,ndqxhz1lgu 4p5; h0 not moving with respect to the shore. Is she doing any work? If she stops swimming and meren 405whquhp hdg),mz6wx; l1mly floats, is work done on her?

Is the work done by kinetic friction forces 3g2 briqk crj(fw69o 2i 3kr5xalways negative? [Hint: Consider what happens to the dishes when you2fi 5w 92qx3or 3crri6kgbkj( pull a tablecloth out from under them.]

Why is it tiring to push hard against a sqe 1o4wv16rvyp0 a+yu olid wall even though you are doing no 1w0ov6y 1ypeur+v a4qwork?

You have two springs that yse gr*d q+358p)wjg dare identical except that spring l is stiffer than spr dr+s j) ge3w5ypd*8qging 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 byt ytf5fev/8 2ix0vrn5 l3zs-/mv3nxlock that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and3lft2y 5ri nyzs0/tfx nv5vm-x3 8e v/ 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 dll,z.v9 zc8h j 8 9ao/arjd+ijoes your gravitational potential energy change when you jump as high as you caav d88/oi,r c j h+.zlljaj9z9n?

In Fig. 6–31, water balloons amsmx:ym. 9 l/ ,lwty3yre tossed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impat3/ lymm. lm9sxyw ,y:ct? Ignore air resistance.

A pendulum is launched from a point that is a height h abo er4s/kf2( ,8uou l4fyhuw-oi ve its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m4he8/uf-4 yfswu lo(k oui,2 r/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring bnjr*p9d8qa y- 8t -nhey pressing down with your hand and then release it, can the spring leavenpya j8r -q8h9d*-tn e the table? Explain, using the law of conservation of energy.

A bowling ball is hung froa :d:i sna*qs9m the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stand sa:aq n:9s*ids against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at thms3c8sa :r4qoe top of a waterfall fallsr834ca m:sqso to the pool below?

Describe the energy tf1ppu; 6jea: gjr 82hmransformations when a child hops around on a pogo stick.

Describe the energy transformations that take place8ib6 hzhgp((z*- wtllcx ,4nk when a skier starts skiing down a hill, but after a time is brought to rest by shi wct8(kz4 -z, 6lhlg*b(nxptriking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a himg 0bo ef/zdt04m: ; vq)r(tva93iglbll of height h and slides down. Does the veloci;z(/:qbemv g t0 m0irgb34 )olf9vtdaty 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 falle7*w3en o,txsw n log in their path rather than stepping on top and jumping down on the other side. Expl* w7 w,e3tosxnain.

Two identical arrows, one with twice the speed of the other, are fired into l dubi;kl.)r hd l*s):a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will pene*ld kslr)bu;)i:. l dhtrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) j+ ffa o2tf1s0iuylp r5( 7l*rignoring fri5u+i(r aj 20 p17stllf *yfforction, 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 thansyah)v 6t k0)p its original heigk)thy6apv0s) ht? Explain.

Suppose you lift a suitcase from the floor to a table. The work youpv+ alh:+g+hokupik1c a50k8 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) th+hgkik kucp :av51+p 0+l o8ahe weight of the suitcase?

Repeat Question 22 for the power needed rather thd,obmbb6p5hl;0ss9 scq2 * faan the work.

Why is it easier to climb a mountain via a zigzag trail than tp( k3ssipiw:+o climb straight u :spsikw ip3+(p?

Recall from Chapter 4, 5vyh;wmu3p 7 .uz*wb xr.wqh5 Example 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account foru5vw*w.73 y hbz wh up.xmqr5; this, using energy concepts.

  How much work is done by the gravitational 1axz+ek(hm yqlwh1 ,4force when a 265-kg pile driver falls 2qh1y+eah z1,k xl(4w m.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 mag2n/6yw, x(iiw zj-h/dx m ;aijy9 1j high. How much work is rexy9zja6 jdh2- i(w 1,mi ja//xin;ygw quired?    J

  A 1300-N crate rests on the floor. How much work1:r,4vr0mpp 9ktbmpm ; 2 9httr:tuvt is required to move it at constant speed (a) 4.0 m along the flom,tr:9hvk 9rv2 t0m;4upprt1t: tb pmor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing 48b5)7r z 2bumhntg 8p(oxsx (tzinu3a 160-kg crate 10.3 m across a rough floor withou8xbsg zb)t p24n35 nhuirm(o(7tz 8xut acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a forcer/g+ bbxvuh917 a(hln across a floor at a rate of for 7.0 a/1h+vubng7hxr lb (9s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, liekbltyk*xm39/-q as */fjy g8d flat on a table. How much work is gt* d8//j 3lq yxamsy*b-k9fkrequired to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objecsfzo. wuga 8 (/jhpn1qrc -a85ts we might not otherwise be able to liff. Show g1/ s .oz8fpj -r(a8qc anuw5hthat 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 andgo )b;re*mps, zlbj. ; 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. Ca;)p *s .b,oe zbgrjl;mlculate:
(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 helicopterxffsco 4 q0r3+ of mass M an acceleration of 0.10 g upward.+3fcxf rqo0 4s    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 distancevt.pbe 0lxs-* 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 ph92xacn 9nqajt;, cce.1*gmx axis, varies as shown in Fig. 6–37. Determine the work done by gt2xjq,cp;m19n hn.a*cce9a this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted ojfe)higg, 9 at9n3e/ hn a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with ubfoa8z6 e)/ iyr*7lm1xif/8gdm,c x 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 factor has it ratxd,2tj .:1lg dfd5g )tn+cs speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is req3-gf4y95omodz (1j9 o m eflghuired to stop 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-kgcabahp t (om:m7:r traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fir o.i b1;lj/evqed from a bow whose string exerts an average force of 110 N on the arrow over a dis.q; 1/ oelivbjtance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelinagzh ,t9vk:kgk7 37zsg 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What wasazg:k vk hz,3k 7gs9t7 the average force exerted by the ball on the glove?    N

If the speed of a car is increased b0y b/y*s 449yqdiupc*0vbg +a u qj)lky 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? y*+0pvjub uc4 yys9gd *ikqlq/ ba)04Ignore the driver’s reaction time.

  At an accident scene on a level r*+ ko1)ypfzn :h7c8pala v):f;p tt,a pzt0cw oad, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.4 7vt:,;hfpkw a)ptcotn)8pyca0:+1a *p fzlz2. 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 reachlu4,/milaa o3z(:ji des the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance bet(idm a :uazl3li,/o4jween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown s* yhx.77(nf umie6qpetraight up by someone who does 80.0 J of work on it?p(mqe7i*nx67 yuhfe. Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a sinwj5pt74 gp qp3gle cable. Determtpqpw7 5 j34gpine
(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, +o:n,kfvt8 q eof 440N/m How much must this spring be stretched to store 25 J of+,f:eqo8kn tv potential energy?    m

  A 7.0-kg monkey swings from o)o(6o65m od.ujut4e g loj qx7ne branch to another 1.2 m higher. What is the change in poten)ox67glm (e tu 6oqo.5jodju4tial energy?    J

  By how much does the gravitational potential energy of a 64-kg pol/.d9m nhul7vn e vaulter change if his center of masu .9/7nv hnmlds rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 606oqa0mg;* ez.x vops5 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness consta0v x*;se.oq0m a6pgoznt of the spring?    N/m

  A 1.60-m tall person lifts a 2.10; c.q*h5dig/lhe2 cv3 wwwsc4-kg book from the ground so it is 2.20 m above the ground. What g4; wdsh/ic wlw*qe.ch v5 c23is 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 aq s:zob/wzio, z+k .5w7krpl9n elevation of 1600 m and climbs to the top of a 3300-m pea/:w . 9ko+pkrlsi , zzb5wqoz7k.
(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 verticall/azq ymo6 b2. ub8)lsz 80mvlex8g;.n d mjdy.y next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If .nv;uz xyz.. dl8 lmq8d2 0oey)jm8ga/6bmsba 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/sd1bqo+fa)kfjr +ac. 8 x6x fk() and grabs a vine hanging vertically from a tall treek+crfxkx. 8 d q( +f6ofajab)1 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 u;n *;mnp jhd0ct5t 0zdown a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictiohlf eay70/4a+0tejr wnless 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, Fraqa/71 m.bts4 w lnqa2cn’s kinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimu al/ 2banct1q4smq7.wm speed must 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 artist jumps vertically upward from the top of a platform isisbcus 1fe/z- t(0)with a (eft / su)i-0cibzs s1speed 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 sttuumn4x2c l.,l3w r1tiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) Wha3r,ll.u1w t m c4unxt2t upward 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 slidez ;gh5/m)lyyq9 t dls6s without friction along the looped track shown in Fig. 6–39. If the block is to remainthm;6/q zydg 9l 5)sly on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (sprinvv c:; iyw61 /54 vjnlqlhix1v0ku.kbg stiffness constant k), Fig. 6–40. The block is given an initial displaw i11ncv/6. vlhkxy0vj:bu;l i v 5qk4cement $x_0$ 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 z jx+1 ue/ wmpi;/gpxehd dp4, )v3kj)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 stiffness constantxpi3ke /+j)m ,p1xv gu; /)dew4djph z 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 shogl -x 6so2jb(vwn in Fig. 6–41 is dragged up to point 1 where it is released from sgvj6x - (lo2brest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a s20 usc4 m+sqxnpeed 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 designingl+q mp- 8ry;eob8 2oe74fibed a spring to be placed at the bottom of an elevator shaft. If the elevator cable should breaib-r28dy4 el78+e mp;boe oqf k 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: a+t s0rda1dt 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and tqq ).glgzqcq ls0(c11 raveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in lqg1(cq sg1) q0.lqc zthis collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wib;:qbs2 )qh lmth a speed of 2.2m/mb;h: qqs2bl) s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest ax urt6t+ e :p:rhmxg//nd slides 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 13.0q,h 6iag0onvx g ;-u,d m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m,sccufsy,2s 2 r c,2(io and it bounces back to a height of 1.5 mi(s c2ocf2sc r,,u 2sy.
(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 re9; i48 oomfftr kxh2*pst, 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 coko pm*9 fxf4h;i r2o8tefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 withv s5,anjc9gv o37fql4xv0 g0k a speed of If the averag7qngvj3s,540 ogk 0a x clvfv9e force of friction is 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 reaches the fdag vbqsff2h 2f75m4 nunw8 ).oot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very 63rbjih bp f-94nu)*g wqv 1 fsz(nek9light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring s(4v9z n f n)kfwq3g9sp-he6rbu*ij1bystem, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal s::t-6nyts jb jpring, 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 position, how far beyond its equilibrium position will it strets-b :jttny 6:jch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass oo2e;14-ji 2x5u*xkdnq lucg ulksj( 0f 980 kg including pilot) that was launched horizontally at 500km/h from a height oj*kull12d 0u;q xkojs5 u cgei-24xn(f 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-W motor to lift a 315-kg piano to a f +6/rytuxdj o 50i9jvsixth-story window 16.0 m abovx0i j9tvu5/frdyo +j6 e?    s

  If a car generates 18 hp when traveli2:xlprs i,t8b2f.e vn0dwnl/ ng at a steady 88km/h what must be the average force exerted on the car due to frictiov r.n28 2l/0dw,tlb :isenfx pn and air resistance?    N

  A 1400-kg sports car acceleratpqd 15v 1ktm+v2w27hw1 *pqf6 pxvvh jes from rest to 95km/h in 7.4 s. What is the average power delivered by the engin2 wt11 qxqfm* 1vvhwv5k vp7hp6+dj p2e?$\approx$    hp

  (a) Show that one Britishn 8 2vm +lg,0i7etxnsd 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 arlw.l+cl ppc.0)yhk f 0e often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-,)q al-x 7adp;p ;gyjtkg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.7,-xqg pjldy t;p;a) a    hp

  How much work can a 3.0-hp motor do in l +)-,ik / bl0uqcg+j5xgvj h2wbp7mz1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this m dupq1 bz;6dy6otion takes 1.5 s, what ave6d6qyubzp1 d;rage power was developed?$\approx$    W

  A pump is to lift 18.0 kg ofu) elwas d-ey*t4a +w+ water per minute through a height of 3.60 m. What output rating (wl-tee* yw 4+)wd+ua saatts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadiug c 1)dwc-o9krg3blyzsiw/bve23 :b7m stairs in 66 s. The stairs are 140 m long and inclined at an anglr/)w3b :e1- 2dkics9glo 3by 7czbwvge 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 porh -zt;2v9z 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 )oxart )yp-j16kvh +rcan it climb at a constant speed of 75km/h if the fri)otv1hjk +y6pr-a xr )ctional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a moto3 zpi+m4s)bbcu+)drpvsi, k 5r have to be able to drag a 310-kg box along a level floor at a ss))cubi 4 5mdsvzprkpb i3+,+peed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down )hab(fs x(pwddy8d3t3bnm5ltx n 5k 8rht 481a 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 designea 2*9 o4 or*)iwwklbkrd 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 k ko*r4ra)*wwb9 oli 2the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm offxuyi( izmu/dy :,f.. n6xat-lcg s0q) 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 216 .n)isui .c/(agfx m-,qzx:0lyt uyd cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famounhmq-o. eo4t sj5hjri6-ihu 7 2-t/qxs long jump (Fig. 6–42) in the 1936 Olympics shows that his ce toix7 ijnq-uj.m ht24hs heq 5-6-r/onter of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m slidingyqzxq;hl:75td) vr l0 without friction along the looped track shown in Fig. 6–39 is q: ytrqhz 0lxd5;l)7v to remain on the track 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 an aircr g52ur)1a -cwfacs7ca aft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his termiaag 7f2w-ccsar5 cu)1 nal 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 Lh*ia/t n3/ cby whose other end is fixed (Fig. n/bh *ct y3ia/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 ux:e;g -qhr+oclimb is made in 5.0 h starting at an elevation of 2300 m. Cahogr-;x e+:uqlculate
(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 br-qfmgo+wa (8xeaks when a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in Califorl78 ggc9w.*gxd- tk pvnia claims that its lifts can move 47,000 people per hour. If the averaggtl8*pgk.-9g7 wcd vxe lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls,x j 5ljr-::s)af8ardctj k e0 vertically 81 m before striking the turbine blades. Cal,s akjcdfjlxj 5 :0e-r8rt:a) culate
(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), thb1bchd 9man, gx(2zk+e 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 wbamb+ nxg( ,z 21hkd9ceight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how high (i)mspwjav(ik0he:v 6 nb93u could an 82-kg man climb a i3wsh(ibkev) (u n6 amp v90j: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 angluzd(b g3;th.alzi v93 e 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 t8 l6s) u.bxewwq 1bnxg8q*sd 2quji 8(he scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale(b) .8ux ew6g undsj qi8*l8bs 2qw1qx 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 swil .gj q( 57kkk9euonx-ngs out over a lake (Fig. 6–45). He releases the rope when his velock75qn(kugx . ok-9ej lity 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-kw anpugx,ifv6*;9) nw0 taaf.g athlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to acg pxf9f u *vn.0waaitn,a;)6wcomplish this feat?    W

  Some electric-power companiesz(rq( 8 h 9ubsqyb-h/d use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir(9y/zsqb 8rbq du(hh -. 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 spring 6 7.4mfw km csdv o(6*di:dyecstiffness constant for each of the two ryed(7f mcw o:dsck6 . d*m6iv4esulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 33v;j,bbkp v rrn6( ju-7 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long (a7 kzvn/q ;9kmf7vdewill it take to accelerate from 55km/h to 75km/h Assumev k7em 9;/zaqfv (nd7k the power stays the same, and neglect frictional losses.    s

  In a common test for cardig9bewbs t 8(4tac function (the “stress test”), the patient walks on an inclined trea g98b st4bwt(edmill (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 distance of 500 m, w- jx t-)jr3hxghat was itj xgr)--jh3txs velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a watery(p rzse x8de4:rs9z7 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 output, what is its maxip(zx r94sysre : e7zd8mum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s