In what ways is the word “work” as used in everyday language the same as omkd x,x x. zl:ou lf.9f9 .gp6uxm-,wthat defined in physics? In what ways is it different? Give ex lmkouflp .6 wox:,.9.xdux 9zxfmg,-amples of both.

Can a centripetal force ever do work on an o; *yye4dtj/ dwbject? Explain.

Can the normal force on an object ever du.xzc(9 l :9 mp ace95itgdlz2kghv; ,o work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doing ;z6kv 21h.bcbe 9. myi1ajwxtany w yvix1h.ta6 m.ecbw21k9 zjb;ork? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? nj- lppj.nvco; 7uu,g.1ptn9 [Hint: Consider what happens to vg . nu, jl.c1pnuo7ntp-j;p9the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall ow1husee36s 8qz /a5 keven though you are doing no wo uq8eazew s5o63 sk/h1rk?

You have two springs that are identical except that spring l is stiffer than u) 8chb-h0+ n3rnvriusx)tw9 sprnsi9cx3t) ) 0-+rbhw urnhv8 uing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to sli.t1f:-bu9 h3 jcaftbw de on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has tra.h13tbj:cfu bf -awt 9veled 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 g:-2. 0 uxu c ho;getvrkdnlqw9;mnu,: ravitational potential energy change when you jump as highx0u ocwu ,ngk t;hr:lnvu;:-q9 m 2e.d as you can?

In Fig. 6–31, water balloonsk4 )*rt8lb.yu6htryb are tossed from the roof of a building, all with the s8l yy4th.)k bub 6r*rtame speed but with different launch 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:nofvv0b h0dryq6d2 ) lowest point in two different ways (Fig. 6–32). Durinfyd :)00bvh26od vnqr g both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring (r-.r u)x.dvcnp w,lx by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of rxn .d,)ulw-p(x c.rvenergy.

A bowling ball is hung frkjq: )hxu9h24(bvaf e om the ceiling by a steel 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 to release the balljxvqua49 bkfe:2h)h( without pushing it. Why?

What happens to the gravitational potential energy when watm lcyojzx2- nf s7oaz 6*t41tk;; y3joer at the top of a waterfall falls to the poj 7*sj3 zl ct;t-a;yno6fyxmo4 k21zool below?

Describe the energy tr2x gu;p1l.;v d3,po8eqmpe f(r zac(xansformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skii /s1 q1v/ogn fjtxq(e*cwe g45ng down a hill, but after a time is brought to rest by striking w5gn/ 1*4vqjfxsege t /1o c(qa snowdrift.

A child on a sled (total mass m) stac.bowwwio1*bds8 0ha i qj nb+*qz8 )8rts 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 hillio+h s q*q8b0. cib8odz)*1a8 jwnbw w if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to ss4z 3yo8u3 v: yhzfdq+tep over a fallen log in their path rather than stepping on top and jumping dsyzfq38z ovh+ u3d4:yown on the other side. Explain.

Two identical arrows, m :u*a x,svejw) z-gq)one with twice the speed of the other, are fired into a bale of )eas zmvwg-)jq: x,*uhay. 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 simple swinging pendulum in terc3qrot w157b z ns/pi3hydkf313k w 9mms of energy, (a) ignoring friction, and rb5smkw f3w3t1o3hz31d yn q /c7 9ipk(b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebo;i tbk, ;d c+h+iip;v4wh gw:eund to a height greater than its original heigeip+4iht+w: ,;;whiv c;d gkbht? Explain.

Suppose you lift a suitcase from the floor to a table. Tha5;thk8f kx xr6t6g /he work you do on the suitcase depends on which of the following: (a) whether ;xak ktg/65f r8hxht6you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than thgaw(;)+xd2q fcxqn0no h 13zse work.

Why is it easier to c+qvs5jm1 aij 5limb a mountain via a zigzag trail than to climb straight up vm51j q+sa5ij?

Recall from Chapter 4, Example 4–14, that you can use dmjo-hb 6 n28ua 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 for this, using energy concep b68hdjmu2on -ts.

  How much work is done by the gra1 9uh cox l2o811ud 6jtvcwvn0vitational force when a 265-kg pile driver falls n1hcv ocutxlu0 v961 wj8 1d2o2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs, jaubk. ho;o* 20.0 m high. How much work is requirho;o a,ub.jk* ed?    J

  A 1300-N crate rests on the floor. e +o2wkr:v.e+y0a a lyHow much work is required to move it at constant speed (a) 4.0 m along the floor against a frictioo+y l2eraw +k:yv.0ean force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movb- r (*0gh7g.l rhle4esy1ctn ers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction hn4 yth- c(sl1* e7gler0b. rgwas 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acro ;dmgc3lb+k //qxf9dn-/j sv zss a floor at a rate of for 7.0 s. Find the net wor/gv/ -;fdsk /jznxq3m lbd+c 9k done on the box.   J

  Eight books, each 4.3 cm thicdtb wmf2s3zoes)+wf:r) ,p . vk with mass 1.7 kg, lie flat on a table. How much work is r 3fwps f2w,ervb)smt:o +d.)z equired to stack them one on top of another?    J

A lever such as that shown in Fig. . ssa;i)rtu.e6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output force, s;au..est) r i$F_{\mathrm{O}}$, 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 fe( 9r/h:cbzf brom 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. Calc(h9e:c zf/ rbbulate:
(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 helicopte(5kv(t2uwq t cr of mass M an acceleration of 0.10 g w2vct((k5q utupward.    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 distblx+r t moh029ance 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, varies as shown in Fig. 6–3l 9vvd/02o (;nxhdb qjh23zdf7. Determine the dn/2jb92z( vdf3;0 ld hqhvoxwork done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on adlj4 a(e xut1 erk29s i;6ms0p.fyth 4 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 mass ofu;sp8 ykd uk2h/ d-mg- $5.31\times10^{-26}$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 its speed increased? d;i mqziiofcr9lx46 .8p/d .n $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elio vvt 8ub qds8hh z87:is;ri xn401d-ectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 125::lh;6rzeai6g v)alh.ug l) p 0-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average(:jf,bi/-: ea*auqx wy d3une force of 110 N on the arrow over naewf u,*qu eyi:-: /xba3(dja 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 77qr/q2w h5mi h1efga’s glove backward 25 cm when the ball is caught. What was the average forcerh5h ge 7f2i/ 7awqm1q exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum b -, b7sae),hih lisuev+.m0l qraking distance be . +mb0,7lsau,l) iviehs-qe h increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investm3 pnot(pyi; n73jxs )igators measure a car’s skid mark to be 88 m long. The accident occurred on j s;pypm) (3noixn73t 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 ey-; h rx9 swj53sr2xnk pko8:0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity,ejs xrr-5x8 k ;kyp3: wnhs29o estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go ifcm3f+;arg d h; thrown straight up by someone who does 80.0 J of work on it? Nehfgmd+;a;3cr glect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accelerat4k 3u 1hgavb )5ggvi 8u/zl 4jxng*,rjion by a single cable. Dete1u,v/lgnra4g)kugihgx3v* j 5zb 8j4rmine
(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 stiffnessj. i-ng gg( 3)*jh4csnudr5z b constant, k, of 440N/m How much must this spring be stretched to zj- (cni)j gus5rdnb34h*gg.store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is t g +g/nyxpw)/qhe change in potent+ gn/)pgxw /qyial energy?    J

  By how much does the gravitation6sr0l 0o dvqt:al potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the qdt00:vlo r 6sjump?    J

  A 1200-kg car rolling on a horizontal s b9yh.9ztr;t a g,k4mdurface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance 94 m9g kyt,ha dbr;t.zof 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 1zrg 4(v.2bz c0t ctd( )vbzlb2.20 m above the .ltb vzbdc0z cvb(2zr gt(41 )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 and climbs to the top dlu+* +pybehsd bg791of a 3300-m pbp7uy e9g* hb+d ls1d+eak.
(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 pp9g83 4 icwb krrv4l(hangs vertically 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 will the end of the spring line up with pr4b4k3 vc 9w8(plirgthe ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (;fmnk:m,bo +k5.3m/s) and grabs a vine hanging vertically from a tall tree knf:km;b +om ,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, slidesrpj :s:nv. am: down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up akxlky6is3k60 bg;-pn frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformer9 4tzj ajyt2:d into gravitational potential energy without the aid of a pole. With what 2: jz9arj4ty tminimum 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 artis, rzwkfy ro*82q1gfnf5, r)c kt jumps vertically upward from the top of a platform with k, g,zy r8k 1rc*offf 2wrn5)qa 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 (igndjcai m9gj- v5e-o;(vore its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What uije5vmcd9;vj a- - og(pward 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 frie6h3xwl9xh b-+v izaq 2 e9qutfv)81nction along the looped track shown in Fig. 6–39. If the block is to remain on thxq98i3elaz bw9unh2v v6e1fq )x+- 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 (spring stiffneib*ycr zgm.) x8;4:fpc:mrr yhr3l; zi q/y0y ss constant k), Fig. 6–40. The block mz0;xilzcmyy;/g. 3ryc4hfp)rb r* q8:iy: ris 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 fn5x)i5 cp5jgtq+ otm6 r.op 6urom a bridge. She is tied to a bungee cord whose unstretchejqpo6 nitxo g55.tp) ucm5+r6 d 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 applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car sho)oqcndbgkp w./*. )(o chyn1bwn in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no fricth.b yb1o n*c.)/(w q)pdknogcion, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angle of 33 m-lgk 3 ox1yg8$^{\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 j(7 5f v1ldfndbe 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 dnv17 l(5ffdj 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.tc.4bfb2p.p2 kxqzw s7uv. . :) ivqtl8 $^{\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 qbp yth5 /ou f5ilh.:8of mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this ip tu:yqflh 5h8/b5.o collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a speemz;9xb+9ip o vd of 2.2m/s How much thermal energy due to friction was genv ;+b9xzi9po merated in this process?    J

  A ski starts from rest and slidesj 9lcgy6a/e shhaa)0: 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 droppo 5q12d k;fqz-3jojsyed from a tree 13.0 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, and it bounces back to 4d(ann sbrk7piqsfn2q9 ; 6- ya height of 1.5 m.6nipy9srb- sdqqk 2(n; 7af n4
(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 constni7irz sb pq+(*5qxanz9v 5/ dant horizontal force of 350 N. For the first 15 m the floor is frictionle n+r55nz /7zaxi9 d *vs(pibqqss, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in p g0wxqpmv1a*wd *zkhgv+m2-.6pu-g Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, witwgu*6 zg1pgppd2* -.+vmq -wkm vh0xah what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches th l;)w qd4pi*6y 45clx(c1u)x hwiptzg e foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal sproo2, lp-i,2xn wweca zxf611aing (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equi,wflnzxp x,a1iw 612o-e 2coalibrium 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 lighmo p7 48ptc9bqt horizontal spring, Fig. 6–40. The block can slide along a table where the q 489pmpt7cob 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 shtgu07 vjq(.q luttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resiqgj q0t(vul.7stance?$\approx$    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 sixth-ston+.(x nd d8t;oa7vtevry win+8 o;7 vdnvtdt.xa en(dow 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h wv7 .*o1 lrionbhat must be the average force exerted on the car due on1r l*b7o.vito friction and air resistance?    N

  A 1400-kg sports car accelerate ouphumf :+f-7-h /bifs from rest to 95km/h in 7.4 s. What is the average power delive:7 bph/u mh-u+-fofifred by the engine?$\approx$    hp

  (a) Show that one British horsep). syc7n;b+/j5kygu2 apmzo8z9 rnzkower$ \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 “ksxeq63:h b5cap: kq31/bexofbn2r 3milowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car s 6ti4)pi)ab kfwl/dv(lows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts k l6w fa)) dibi4v/(ptand hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h?aw 3y 0ev:ge:m $a\times10^b$ J a =    b =   

  A shot-putter accelerat4zbyvg(b4yug6o z;d : .tlb0j es a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what a;g b4u:4ybz(o6 jb 0yt.zgl vdverage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What od**gyp:ga - zfr/w2li;ip 5nxutput rating (watts) should the pui* g -f l5dp:n*w/xga;zp2irymp motor have?    W

  During a workout, the football players at State U. ran up the stadikv/ 7b ,iyzy;bio3 em(tll 1.xkk )my2um stairs in 66 s. The stairs are 140 m long and inclinedvz3m2);olil ,kyb e(y m7.kb iyxk/1t 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 cycli+2lou a7serk- x( 1obost 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 1206h1) jctp:uywtzsc0s u 8zy6 pzg0:1z hp. How steep a hill can it climb at a cons1)s zj:6sw:chptgu cpzz8z t 0y6u 1y0tant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower mflp:8lc h09 3hdj+hqi ust a motor have to be able to drag a 310-kg box along a level floor at a speed l9 8d ip03+hlc:hhj fqof 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down zdxt, s8d/l5h q0w,xs 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(8km/h) bumpers” that are designed tsn ;z4r uwl giak022u:o 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 consi;un 42ruzw:a2sk 0lgtant 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 isyv- am/mct p/ j,uypig)s4 64p 10.0 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 pv6yy//)pmg,pc4 4sju- aitmholds 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 f j:ipw1n2va( aamous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from laun wpvai a(nj2:1ch 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 sliding without friction along the loope/5zw bn*-gw9 i y*8b(qeomxcj d track shown in Fig. 6–39 is to rema z9b qe5b*wcmy*8njw x/iog-(in 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 jumpia5j ,cnk+3tqo8pw 4uzng from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only mn53 c4ko,j8tqa+ zpwuinor 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 othltac7ee z3 cwrqd 3+,2) *u*yv* kppfter end is fixed (Fig. 6–4ka**l*fe3rwc 2) p +zuyd3 epq,vctt73).
(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 nx 5do+t8 *.l1tijf0 tmp/e1hi -9wwj) xfjxe3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 230w0/wj -jl im 5+1j exo)p9exti nx*f f8h1.ttd0 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 whenic:unbif, +r61kg)jhic2i )g a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can a e mu2cgto8 u(m:.2lqmove 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, eulum 8amce2.o(qt :2 gstimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s andt9 r.rsg/x1 hi7y5bdq falls vertically 81 m before strikin5q/y1brgri 7xh.tsd 9g the turbine 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 rollej8 /qywt830mh ypbu7wk;4w bxr coaster 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 t3uhwby 88/0qp xbk4 ;mjyw7w. 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 * g.ec(;l4zjlsao;y86y g0n7 i ofrue a candy bar directly into work, how high could an f iyjn 0 leoog sr;7.;64yg*ezlc8 a(u82-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at 6(+km7lyd xi)i cfr0e4 m8iewan 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 compresse9cq(x/0tr qpn s 0.60 mm, and it tells you your weight is 710 N. Now if you jump on tx0t( r9q cp/nqhe 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 out over a lake 0mt7 a (g bh664k:k ud*j lficn0vbdb3(Fig. 6–45). He releases the rope mfh6dkb*(406bv07u jn tdakbic: gl 3when 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 a y6*so6 fg(r6(leibtnb/vu i/thlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to acc6 tnbevfu6blrsy/( *(og i/6iomplish this feat?    W

  Some electric-power companies use water to store energy.p ac* )f 9a/pbiqg*hy/ Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy prodpih//pf)ay*9cb ga*q uced 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 c*q.)1gh vn *fk4lr vfwut in half. What is the spring stiff4*gkqfw. nf)v h*r1lv ness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m upxu4or:cje p jjgx/, k6 fi* rkek1s+46 a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long will ixaaj)m.xyxj*mgj7x pa5 9.2lr /w 4 dgt take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect friax5.jdxxg.4/ 7l *wa)2jpgya rx9jm mctional losses.    s

  In a common test for cardiac funqslz5t, no48dp3ru+e ction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimalz8,r4q+5od3u s np tete 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 voxuq i*axedj 5ki79d+v 28):: kpdmf 41wiau500 m, what was its velocity when it left the va )kdxp9a7 8owduxkf*i i 5v4d:: +1e2iv qmjuolcano? $\approx$    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 6q46 ;uc(;h uflawg oqewhv+2height of 2.0 m at a rate of 95kg/s (a) If this water wheeqe;l6u+wv 4 (ghfquch6aw2 o ;l is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s