In what ways is the word “work” as used in ev wg wxq+miep.3,s: n0ieryday language the same as that defined in physics? In what ways is it different? Give ewn.s+x0,empg:i iwq 3xamples of both.

Can a centripetal force ever do work on an object? Exer:o; aj y0r7fplain.

Can the normal force on an object ever do wor-wz;ko km ;zf*k? Explain.

A woman swimming upsthr2 wnt fd +cq)l2gb.+ream is not moving with respect to the shore. Is she doing any work? If she stopbr2ndc t lw.gh)+2 qf+s swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwqo -vw:hp 2mrd,iu8 sw*xt 68rays negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under th8mrw 2sr, uit6-:v*dp8wo hqxem.]

Why is it tiring to push hard against a solid w.k-2iypp zis;5)ymh e+ )en+rasc f3 gall even though you are doing no work3ais-ky p+c ;ifp) )2yrs 5ze .h+engm?

You have two springs tha ;tt73retp4xfgtdx :7 t are identical except that spring l is stiffer than spring 7f t exg7x3tr4pdt; t: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 tvdr objb1 7de+)qc5n( t;q /gyo slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has travele/e vq+ gb(n5do7)1ybqjdr ;tc d a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change whwp ndapbd( u ( 937.cjkdjnj;4en you jump as high as you ndpcjduj a4 bd9n kw7(3.; (jpcan?

In Fig. 6–31, water balloons are tossed from the roof of a building, alqldk ,e0oo99m l with the same speed but with different launch angles. Which one has the highest spkdm0q ooe,99l eed on impact? Ignore air resistance.

A pendulum is launched frozp x(wy5wgs9r0+ wu l;m a point that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the penduluw( ;g wzw0+sxy5 p9ulrm 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 upri wjh(6 l-wi6)ix xeki*ght on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the tablxh wwe *j6 ik)-(xi6lie? Explain, using the law of conservation of energy.

A bowling ball is hung from the cwhgl05 xzi0:4 6wx rireiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball agi4 wghwr 5lx r0:ixz60ainst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the 96wrtdk8upielh(5e) gravitational potential energy when water at the top of a waterfall falls to6r 8udlpe5wi) k9the ( the pool below?

Describe the energy transformations when a child hops around oc9wp -*gi,xhz n a pogo stick.

Describe the energy transformations that take place wh1jwv*opg l2k7 9s5rhzen a skier starts skiing down a hill, but after a time is brought to rest by striking a snowds opv h95g*2rw7klj z1rift.

A child on a sled (total mass m) starts from rest at the top of a hill of heigh9)p9ak2 zw9 sxyga4fht h and slides down. Does the velocity at the bots pkfza9 h4y x)a2g99wtom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their paz qo6b1d dql/) 1dv9bkth rather than stepping on top and jqqd /kd69o11bz l)b dvumping down on the other side. Explain.

Two identical arrows, one9(qzvh x4xl793vjkl x zql2g5 with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on vzxk9 (xv5 h2 qgxlz 94ll3jq7the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms ofwa2 8sf ruw3+l(6zm1i v ktmvey354sr energy, (a) ignoring frictioss4 kmf1wu8a v v3z6t rywm52l3ei(r+n, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can itvfly(iz g*/w/ rebound to a height greater than its original height?zwivlf( / *y/g Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the 7/gbh-5f sa2/azqujm 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/j 2b 7agsf/5azuh-mq (d) the weight of the suitcase?

Repeat Question 22 for the power notn7ajlk)9,afg;v rc 7r7yu / eeded rather than the work.

Why is it easier to climb a mountain vttln *x3uk,k2o pjk,ked,r,0 wib/n+ ia a zigzag trail than to climb straight up?t kkr, i 0nw/pldt kxekjn2o+3,,b*u,

Recall from Chapter 4, Example 4–14, that you can use yp f cg221(izpa 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 thip2p2(cif1 yzg s, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile d; ef k*52zal .usk) nxxzf*jt-river falls 2.80 m?k 5)x tz*.jafenu-;2s*zk lfx    J

  A 65.0-kg firefighter climbs a flk v7bo60 t.btkight of stairs 20.0 m high. How much work is required0o tkb67kbt.v ?    J

  A 1300-N crate rests on the floexzxro9b -b2ow.n as ;t6v5j6r4ahu8:2hz epor. How much work is required to move it at constant speed (ah o 29w5hx oaape2j8;nzx6z4et6 :u-brbsr.v) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crmm 5,mn wyi81u zuq-v4ate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wasmm,v1 wi8zyq-54m u nu 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of fg6eq n+tl1o12095 my;ehcq shclu t u9or 7.0 s. Find the net work done on th ;ee0q 69gstlh1u52+nhccty muo19q le box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg( jv9a en:oeoa1s(y;oe( +ohx, lie flat on a table. How much work is required to stack them one on top of anoth9+o (eano;xvs(1aeoo(he :y jer?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we migh*f6p w(+3b;m9r3s renpchx t gt not otherwise be able to liff. Sh;p+r s(en px3 tb9wc 36*fgrmhow that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accelerating bz2z gbvswtx6y4+ s ;,hy at,vy4z x;g2bhs wz6+s man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acceleu4c+t8kpoz z-o qcy(c)iu t9:ration of 0.10 gu9 kqc(t cc p:y4)z-8tz uioo+ 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 thc, ciuw xteo,3f3,0t;5 tk drle distance 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 Fig7 5lajk1c m,:t( jglpb. 6–37. Determine the work done by this force to move the object (a) from x=0 m to tglmb1lja,( pk j c7:5x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle actlv s e:hm-od32fg*uwj2 s8tm3 s 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, wr e 2: obbi/dk-abwn0h+mk4f) ith 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 its speed increased? u9tkj . *hp.h7 rhyh (oq9;znrr1 (baz$ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop hukvk6tgv;6kand lae70n--1an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 1r s96aaute 3f905km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an avo;o5ym-.h:nv,zmk0nl q i*mjr9jta2 erage force of 110 N on the arrow over a distance of 78 cm. What is the sr:zlt jmnq.onmm;*0 ,h 5jvyk9a o-2i peed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a: b; wul4;euzp fielder’s glove backward 25 cm when the ball is caught. What was the averag;ubp;4 zu :lewe force exerted by the ball on the glove?    N

If the speed of a car is increased by 5be6uo0u6 s *ue0%, by what factor will its minimum braking distance be incue s b0u*ue6o6reased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measurecc(aj/u/,u6 i k t-br/hmgda8 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 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the cabc raki/, -g/8 hcjam6ud /(utr’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at dwm x875fq 9xp vznca92ge*9t By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, est 8nxa9wgxtdq7*e 52m 9v9 fpczimate 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-kf ) gm 9gv0f5o,kdwwhl0*o4 eag rock go if thrown straight up by someone who does 80.0 J of work on it? Negle0o504wm)v9ak,df fweglgho* ct air resistance.    m

  A 285-kg load is lifted 22.0 m vertica,h t9f,n6;u8 zxc;thzqizy1mofu1 k0 lly with an acceleration by a single cable. Determinezn6h ux9f1km8h, f1t;0i coqu,ty;zz
(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 stiffnessuqxa. -za:r+.6f dgun constant, k, of 440N/m How much must this spring be stretched to store 25 J oq z.6r+ d .agnu:a-xfuf potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Wod44p scvb no/;b+)nv hat is the change oo bs4vv; d)4pbc /+nnin potential energy?    J

  By how much does the gravitatid68qw9 jw .pg*hy1nuawbm2)h onal potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jump?j98 .gw*yd2u1m na)hw pbq hw6    J

  A 1200-kg car rolling on a horizontal surface has speed v = dm.31 3fczk,vo2l lkb grhly)wedf+o,jq8( 8 65 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 constyc2lkw gvfbk8 leh13o,m,.jo3)q+ zd( lf dr8ant of the spring?    N/m

  A 1.60-m tall person liftsx*t,pxlgfs29a mwle j 0dm -22 a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the s,tw a92 20-jg2fexlmxl mdp*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 smxqyx1v140e im 3bwn/) i2gk at an elevation of 1600 m and climbs to the top of a 3300-m i0 4 q wx2ynx3be1m)s1kvi g/mpeak.
(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 a ruler. The end of 64 ea+0xgsjft-67 ah -oq cvwh pb*nv.the spring is nexth -xo-vgt w*h0cj4f.6 n a6apvsq7be+ 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 the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine halo1slpvlhpdf9 ;4 62;x rga y2/yvr8xnging vertically6lxav1gl y/d9 vy;2 l8 rp4p2 ;xrhfso from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, stary os6 0s7piynni91k; lt zv(5jting from rest, slides 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 a frip+ tdh f,d49zgctionless 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’su ezvpg 4x,1c+ kinetic energy is transformed into gravitational potential energy without p+ecv1gz4 xu,the aid of a pole. With what minimum 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 tlf;vwvsj36 i9op of a platform with a speed of 5.;i6fw3v jvls 90 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness cons rq7b cn1roez /b35laz;kmk))/gwh c.iy)xn7tant is 950N/m is attached to a table anqhbc).nc)g/wri nbe7r k )z/1ylam3z;x7 5 kod is compressed down 0.150 m. (a) What 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 slides without friction along the looped track shown in Fig. 1ctcf,j teg w)5s :6si6–39. If tc )1si ws5ct:6fe jg,the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring sp x1(;6;qtxo 97ohsb gqrhq x3tiffness constant k), Fig. 6–40. The b xo3hpto;x7shq qqx1;96r( gblock 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 tiesrjqj18sz4 y3f q: ec5d to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungeer 1cqs f4j5:3zsjyq e8 cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1526su8lfrfx6s 5i-z0lh ofsm where it is released from rest. Assuming no friction, calculate the speed at point8is mf6z0fflso65 25-lxsr hus
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed ofz-j 4/u5j djtmotl:f6 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 designissth9x:4:0a w*joz+ rd*lfgc ng a spring to be 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 t:foaszw4x0hg :rtc*j9ld* s+he 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 qp;6c2b.(c cf)u4zzhvtvw +sa 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 traveling 95km/h in opposite direct dvga+jmr 0w(1g:l ,gdions, coll0,gglw da vjrm(dg +:1ide head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bot2n(q 2n laxgu,tom with a speed of 2.2m/s How much thermal energy due to friction was generated in this na(nx ul2q,g2 process?    J

  A ski starts from resj/) 9nqwgn:h nt and 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 1n .q*;p;rx 7kcdub4u6)kb i xt3.0 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 a height o ut gz52fo g6l:97egzff 1.5 me79u5go2l:6gtg zzf f.
(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 acros 7h;tqyto,se+s a floor with a constant horizontal force of 350 N. For the first 1o q; 7hsyett+,5 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed o( d1b d(imc+l5 oi1ssof If the average force of friction is equal toci ds1d5ol(mo+1is( b 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 foot of a steady upward 18.0 n z;(xxsn/3 ax$^{\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 horizonkl,j*y*2lv n ctal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turnkv,* njll 2yc*ing back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a ver mu b ou3;)zorujsra9:6 6c5 hnm8vrt2y light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of frictr:t2so56 cru8r 3m9j nm o uavh;)uz6bion 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 /j3och-g e51bmug z k,shuttle 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 woul1gm,u-h/ jb c 5o3ekzgd 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 mo:4sabo b4k6 kheg 7u3xtor to lift a 315-kg piano to a sixth-story window 16.0 kb4e:hs4ou67bgx k 3am above?    s

  If a car generates 18 hp when traveling at a steady 88km8qvjbvt-p+: 8o7becl7gp:x:dzhx 7j /h what must be the average force exerted on the car due to friction and ax7zlj g:j7c-:: v qpe+x8b 8 hpotvd7bir resistance?    N

  A 1400-kg sports car accelerates from restw 1x6w3cin+mt radh,x(: *f vt to 95km/h in 7.4 s. What is the average power deliveredr 3c (tdvtw mw,ax:* x6h1+nif by the engine?$\approx$    hp

  (a) Show that one Brits uay ezjh91-1ish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often.pzs(i7b qwz: pmct.gx2is /. 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-kg car slows down from to 65kx0e0o7trpio*2i,evv m/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 constanto0 rit,v7xvoi02*epe 75km/h.    hp

  How much work can a 3.0d;b)w/ lztzg,ffd / 6n-hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot f64lwb*k bq+nng u:8hr rom rest to 14m/s If this motion takes 1.5 s, whbb wk8+g*:6r nul4 qnhat average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Whatzkx mr)-x q k49hhg5,n output rating (watts) s rhg xkhxm,-qzk9n )54hould the pump motor have?    W

  During a workout, the football playerazc; v; r l+yi/ecz8p.s at State U. ran up the stadium stairs in 66 s. The stairs are zearz; clcvp; . iy+8/140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb aiz9,sekpvqhxlfm: 5- jm :42o 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 maximum2izeha)kx0(yma aje+mf57 /vu.cx q; power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces a u/m)(a2z x5ij+ eyq aekh; 7a.c0xvmfdd up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg bj 9f-501u v yplbp:xf)7n,f jelqa pe2bdn1j 7ox along a level floor72ypvelb7fpjl-n,j a0 uj x5bd1 fpe: f n9)q1 at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a ).keht)tmzif u60 h 1g7.0 $^{\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) g vabi6dy9n; n t*3;zjnkztgj46j8*qbumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after aqn*z y; in gbza4vtn g698;*j6j3 tkdj 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 mb5-loq0(yszi s88 cc shelf is 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 1.88mzo5s sbc i(ylq0c -5 kg with a height of 21 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 famous lontx+ eh2lftx(a v lmh9 174bbk9g 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 was traveliktlh+9 9lb1t4h2 af x7ebm(xvng at 6.5m/s at the top of the arc?   m/s

  The block of mass m slfqfxc7ny4gtd9ng/s *27x gm6iding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at x*2sd7ngg69 tq 4cy/ffgxmn 7the 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 mq)uh+hy bf1l) after jumping from an aircraft without his parachuteyb)ql )u+h1fh 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 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 whhl8 fm)ofk6krtk7, ;/3gusrm ose other end is fixed (Fi7mk rol fh,/gu6k3)r ;8mtskfg. 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 ef o 3vrn1t7)m/pjm 5.fe+cao-high mountain. The climb is made in 5.0 h starting at an elevation of53om7 j o.nt/fa)revfpc+em 1 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when jx :v.dx)fnl( 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 cl9d.fz5)8bsxy icr)n r aims that its lifts can move 47,000 people per hour. If the average lift carriey)i5zbsc d r)n x9r8f.s 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 vertically 81 rfft-it/i*w ig/qho-5z)6 wa m before striking the turbine blad5ifii* /o-6 ww) rzgtahfq/-tes. 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 roller0 *(5unckgdy b 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. Ignore friction. Show also that as long as your speed is above the minimum needed, t0dykcu5 bn *g(his 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 68 +cyybfhx* vcoulf vcy*6by+8x hd an 82-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 an upwd4 4m/d*2m0rshx7kgu gh7 zoh5groi9ard 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 compresses 0.60 w0,;b mxa vfs91r w9(jv)wapj mm, and it tells you your weight is 710 N. Now if you jump on the vswa v9bw)wrf 901xaj ,j(m;p 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 swingsi-eh5y rpy z76x 5 5jst-0wgpk out over a lake (Fig. 6–45-7s jyph xk 0ryie5 pwtg5z5-6). He releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 1nx4x0(/hau zjdft *om in 9.0 s. What minimum power output was used to acc a4xj/0*zf n1tu hxod(omplish this feat?    W

  Some electric-power companies use 17co7 t pxcpokb6v,2l water to store energy. Water is pumped by reversible turbine pumps from a low to a712o 6ppklx vbt7,o cc 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. Whafi*lnj1/ m;zct is the spring stiffness constant for each of the two resulting springs? zf/*l;cmj1i n  k

  A 6.0-kg block is pushed 8.0 m 9fk-cnct0ky r 2 zy9f(tja:m 0up 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 xjx7 c nk3up*xp1cp / j521murlong will it take to accelerate from 55km/h to 75km/h Assu cjpxj unu7c*rx12m5x p3/p 1kme the power stays the same, and neglect frictional losses.    s

  In a common test for cardif8a k8 a8cqc5ut.p: pltgm1r 1ac function (the “stress test”), the patient walks on an inclined treadmill (Fig ppcafamt8gc818r5tqu.lk: 1. 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-a qvq3c (ef/(l q*jus rbq2p.x cv:1x/kg rock vertically upward a distance of 500 m, what was its velocity when it left the volcano? ccevq xbq/j1l.q(qvas3 /p(*rf :xu2$\approx$    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 heightwe tmh*,v0mktn .0i/f of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to prow0 f vekt*mmtnh./,0ivide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s