In what ways is the word “work” as used in everyday language the same as tha-kbq 4 -cujxc(wbii9.t defined in physics? In what waysw q.ibi9juc(b 4--x kc is it different? Give examples of both.

Can a centripetal force everf i1t1oo-q+g c do work on an object? Explain.

Can the normal force on an object ever do work?vvvhh72i jj; g .h7gf5vpzd6 : Explain.

A woman swimming upstre)omuj c72*c hkam is not moving with respect to the shore. Is she doing any work?*cj)ou2c kh7m If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces b,nbl0 q1 gb9dj*2tl aalways negative? [Hint: Consider what happens to the dishes when ylg jad* bl9t1q,b2 nb0ou pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall evenqx26y5 bx2ofwu/1e 5.c ewntg though you are doing no worcw eyu .f/q2nb562wg 5otx1xek?

You have two springs that are identical except that 0wc pdkx g(/k(spring l is stiffer than springwk (p0(dx/c kg 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 iuc.9y n0uln, spu+ q7bs free to slide on a frictionless su. cy+0qul7b n9nu,suprface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your r9(2 t4ih4o qkfczk*ngravitational potential energy change when you jump as high as you can? n r92cq* 4ok4(fzkiht

In Fig. 6–31, water balloons are tossed from the roof vr dy+-v4xyd ui*4 w*aof a building, all with the same spv4 wx4ru-dv*+*yayid eed 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 h4 rxxo(s qef bpf58- 2yjt64xbeight h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the sec f44fxx t6b8jq(p5o-yserxb2ond 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 resy2f):sf cfe4s ts upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave f2 y4)ef: csfsthe table? Explain, using the law of conservation of energy.

A bowling ball is hungg7ug 8 -bb;nbk from 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 avo7nubk;8bgg b- id injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gr68*0e 7u gh3oi bpavtravitational potential energy when water at the top of a waterfall fallst iv8oeubp03g6 7hra* to the pool below?

Describe the energy transformations whorz1;r2orl - wen a child hops around on a pogo stick.

Describe the energy transformations that take pv bopu4wn;z: gz6)yuc 4/4zcslace when a skier starts skiing down a hill, but after a time isu6bpg4ou4 cn)c4;zsw zz:v/y brought to rest by striking a snowdrift.

A child on a sled (totalh:fnt w2j-7c/a avgz; mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) tj z7nh -act;aw:2 f/gvhere is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pdzam1anhzwoa6 ,p rp a;2 k1h(3mu7)tath rather than stepping 3kwamhzpun6dpz(am to r1h);7,1a 2aon top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired intjk4ps k-906l(pkp1 g:tn-h4i awdxo:kgv; iko a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther wap 4-s0pn(k9 g:t:j4- v kkd61iohipgk;xl k than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulumrfy2z+h re2w8 in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a gr2ez2+h fyrrw8 andfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heightbd1jzb(l/m85mi8mu u greater than its origina 8u8i( 1b/ 5ulzjmdmbml height? Explain.

Suppose you lift a suitcase from the flof+8 lu mw io)/kkbi;l+or to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height +klb k w;f+8om )iui/lof the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the gcy4mk)+ qmt(dah8-f cn j*s7work.

Why is it easier to climb a mounta*wuyq:wpd)*0r:mfiv g jxc6at)**ld in via a zigzag trail than to climb straight upcwugxrtp ))6m*l y vjq*a0i:* *f :dwd?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to de7la cm(h8;vq9qdq g ;gcrease the force needed to raise a heavy load (see Fig. 6–34). But m; 7q v;g8(9cal dqqhgfor every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationkuv4eg3f iyfd3c*j( , al force when a 265-kg pile driver falls (yi4f *3ej 3ucfg,vdk 2.80 m?    J

  A 65.0-kg firefighter climbs a fix,gwqoy8y utu:+yd+( vx 51f light of stairs 20.0 m high. How much work is requiru +fv1: xuxy58gdwi(+ yoy, tqed?    J

  A 1300-N crate rests on the floor. How much work is required to mmuorob x27g/ vh 07+pbove it at constant speed (a) 4.0 m along the floor againsb7r02o7 ou+/ghpb vmx t a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 1-u k4w fk8iz4+w arm1m60-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was 0.50?i-kk4rm8+aww 4um 1 fz    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a ratyf0cia* -qy 3 wa,wp)wmv,4uye of for 7.0 s. Find the net work donempq*iy,wy -0 4)wawya3fc, vu on the box.   J

  Eight books, each 4.3 uylp9 mc. be;6 sh( a5ri)xls:cm thick with mass 1.7 kg, lie flat on a table. How much work is required to stack thec; xs 5 )9ual y.:bp(siremlh6m one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we . hkp,y41k h;oyyoaxh sn18l,might not otherwise be able to liff. Show that the ratio of output fo,n,o.h4pyyxh ;k1 8ly 1k ohsarce, $F_{\mathrm{O}}$, 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 jvz ej/t7; /xiyx,tf/t(gom+7yb ty93.6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effecogy( t zy79/tm/,xji+fj/ ;e vxtb7tytive 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 acceleration 7eu60;)-fv bedn7ks 5g mf ijdof 0.10 b)fgmduein5-6f;e0s7 7vk jd g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is 8dhot q+vyka(d) 1i3.9*loh2aib jv slinear 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. -:fam8y-bk0ic cxvc ;6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 1 v0x fm8-yabckc;-: ic0 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 particlg;(5ee1(5 6mu ,phg tvlbsagqt *)ayd e 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 oxyge szoqxou /a7n- 7rsy ;ewwcid:u07.3 en molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow ib5 knu0bqbi wgbz07owl 0x*82 s doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elpnqx97i:+lh p 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 b,)vii/f;fqm+ / wijiqe done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose sbk9bd0x u6x9 12k eg6 d:odxxxtring exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as 19o0 ex 9gd2xbkxk6x6 ux b:ddit leaves the bow?    m/s

  A baseball (m=140kg) traveling 32k7txf7d9hn(l2xgati c f9y1 +m/s moves a fielder’s glove backward 25 cm when the ball is caught. Wh 17t nl 7fy 29fctxxia(dgh9k+at was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum br zx6)o*a 9able60r q4uoeys -daking distance be increased, assuming all else is the same? Ignoredxaoe4*lz uqe-r6 0oy 9asb6) the driver’s reaction time.

  At an accident scene on a*ywsfsnpec 2enq7l-muczo10 p 88 , 38ardf a: level road, 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 0.42. Use these data to determine the speed of thep:fdlszo78 1cn,3-rq0* 8s8cnmye2a fwupe a 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 ofmh n-***qduut0fwd3y 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, 3h -nmyquf*ud*w 0td*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 1.85-7n+h cxe1j u*lkg rock go if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistane*nucl 1 h+x7jce.    m

  A 285-kg load is lifted 22.0 mw+p6+ 1qnmudbpe nmm vh+e bm 0fix9x-o*.f3( vertically with an acceleration by a single cable. Determi0mmf e. 6e1 *+bqmb - 3pw9mhui xnxdo+n(f+vpne
(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 stifo+73zi p j;wjtfness constant, k, of 440N/m How much must this spring be stretched to store 25 J of potential enerjj+7pt3z;i wo gy?    m

  A 7.0-kg monkey swings from one branch to anotew8xg,bw 0h4xhq + v+iher 1.2 m higher. What is the change in potential48g ivq0ww,x +be hx+h energy?    J

  By how much does the gravitational poti:gt2tu03z w b5oe v/l65*ypbv dxor*ential energy of a 64-kg pole vaulter change if his center of mass risb gbitvw*25: dxo0o yrp3lu*/te6v 5 zes about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kmlk: . za4akw( bz/gtah,9vgcem98lf4/h when it strikes a horizontal coiled spring and is brought to rest in a distance of8z4evzb:k f9kah/a.g,4wga l(mc9 t l 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 pl5m8wo)w x ttf6p, +/rge6 hsbook from the ground so it is 2.20 m above the ground. What is wtw86r)+fp56os/ pgh,tx melthe 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 elevatik2 nt9qhx:n/ o(nsdjz7 9i vi)78lhxdon of 1600 m and climbs to the top of a 3300-m xd9jozh/n72 qthnnk d 8vsi(9x l:)7ipeak.
(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 8.od+lr 0- 0ahqv mv6km,jmb ythe spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of hd 0q6ak8v,r o+ymv b.0mj-mlthe spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top sp1u qjj00c)f, b4lx px/1 impb q01hlw *;lbmheeed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle 4hx;qw 011l /cbb)0jm*fxu 1i,ll0qp pjbmeh. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, start +kc9za.gp:im *1dw fling 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 frictionless 2u1n mq8wb.8ng- 3qaqdw/maf 68.0$^{\circ}$ 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 u m48x(n,7kddg t we5d7s+a htkinetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of masekaxd7 tm7,s(+ghn 45dwu 8t ds 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 w w8aa* (j yuft*qgsc b+h2g6u5ith a speet * squaa*2 bw jhgf(y68guc5+d 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 st5i7lh si 5cy7zltiq(4 y ci35i,jzmn.iffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it g. ,iln 7iyq 5(tj47i5izsy3m ic5lchzive 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 foggq(tk, 9t 9(mrc*aau ,0yzqriction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at thtu, zg kc0mr (9aq9yq*, t(ogae 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 ofr fg-4qsttx0vk3 ;0cl a spring (spring stiffness constant k), Fig. 6–40. The block is giv 3 tvk;glr0ft04scx q-en 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 briwqz8 e*b f6))hx v 4)l8zpcgvodge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a tz)p qfzb 8v )e8gw)6*o4lhvcxotal 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 shown in uete ks :qf/mubrc /:xs)8 j32u4n4rtFig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at ms8q ut)f:4xbue k4r3es/ /2t j:ucrn 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 a(e x6euuj +2f r:ptty1n angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a rb ete: ny :w6.x9,zdcux,v2ft ypp7/spring to be placed at the bottom of an elevator shaft. If the elevator cable shoulp 2:c/9 tbzu ny,x7etr wpe6vx: ydf,.d break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 700qd xyg ct0+y nvo2 31x)yrtd.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 7h e/u5 gf 1;dy6azh)ll650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is 1;ah5z/e) yfgdh 6ll uproduced in this 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 yp1cbs270;qjoo gk a+speed of 2.2m/s 1gq bocay+os p2j;07kHow much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 2-kb8a+k8(t srzjvf,k2ytlr4w4 s t-+ekah n: 2 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the grouoem 9w 20el*synd.
(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 ba 9 ew0 j55fk(o,.l4taaic rgjsck to a height of 1.5 mkfc9e i.r 4a( t50o lg5,jswja.
(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 i s e-0.nxho)a 1m40y,yklucbfrom rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient cx) m ,lby aye1-ki h.04uons0of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Figmmw4gy47-uup l( dbz6 . 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? Thu gzy4m74u- mlwbp (6de distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s re)wl sgf3ya49zk 1itg* aches the 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 horizont.t5ju/uyr02su t s2aval spring (k=180N/m) as shown in Fig. 6–40. It is noted sar/suuv2yut .t25j 0 that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a ver:o 8w c8ya0xxby light horizontal spring, 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 sprin: ac0x b8oyxw8g is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mj 0 j*xhy26ghkass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed h 0jkj26gyh*x 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 8v1 k:wkenfm;to lift a 315-kg piano to a sixth-story window 16.0 m wfv8 emkn :1k;above?    s

  If a car generates 18 hp when traveling at a snoja;j5p(u05 pkqi) zteady 88km/h what must be the average force exerted on the car due to fuqppk 0()najz5 i;5oj riction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the 2g q*h4m psx*maverage power delivered by the *sm*mqpg 4xh2engine?$\approx$    hp

  (a) Show that one British horse)p 5;u(dg ccmquy4n)jpower$ \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 expressweby;a4 u02li ed 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 thasia l 8s eqfl6;(b4n.jt her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts aabj8 f ;ln(esi.lq4s6nd 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? * 8y0d1tqcmok$a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest6irz8 :g /z-ssefwb wy8 uz:.h to 14m/s If this motion takes 1.5 s, what average power wasigb: -z6f whszw.s8ey/zr:u8 developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height eo41ecslwz (:2j s9 s 99hjvcyi4fq;tof 3.60 m. What output ratin9zi21sosv sjwc:l e(4c 4t;y hje99qfg (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the m,x-bun+vh) 4x hw0f,lpwn:c stadium stairs in 66 s bxm-)4,,u+pvhww 0flx nh nc:. The stairs are 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 cycli-5ywy vb txlel+)xb+e7/h g ov40(rrdst climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill c/xl( ol(2dh kvan it climb at a constant speed of 75km/h if the fric kh( ol2/d(vxltional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower m+, j:g6orfppb ust a motor have to be able to drag a 310-kg box along a level floor at a speed of +jbpr 6:gp, of1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0 g r0hf: f2r5oh6pg/zu$^{\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) bumperqdz,, a.jsofmz a41 *dwydo 21s” 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 a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 11zyd., 4os*1zj dfadw2q o,am300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library dogkqlaet :yj*:(y rn2 91ds1 the first 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 1.5 kg with a height of 21 cm, and an average d n (l2gek9:dsr*o yq1tay1j:shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1a+-tv ,l02 bbkc 0vqz6jc (xkx cmp07j936 Olympics shows that his center of mass rose 1.1 m from launcp - 7xk x,6mvtc0 c+zb(cl qabv0k02jjh 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 frictib:0 b.cd9 pcrbon along the looped track shown in Fig. 6–39 is to remain on the track at all timercc b 09:pbbd.s, 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 airc degb kphr71-.vq2 n/hraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, buth- vp.qrn2e d/g71 bkh survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end/ n c03owxid4p is fixed (Fi x3/n wo4pcd0ig. 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 mountjfn 9-mmd3 r0:hni a.vain. The climb is made in 5.0 h starti an v 3m:midh9fn0r-.jng at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevatorkg,akkg- ho 4+-rqca z,h(m7b 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 m p9-b v u.g*iv.kvinq1ove 47,000 people per hour. If the average lift carries people aboutk *.v9pgqi .1nvvui-b 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 m before b,soy- t+3a9a-(jea) lj xuh sl*9 *bowj3l oqstriking the tqs yha3wjo-*9b,l lj*3txa- 9 beosj()al o +uurbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertit903lity0 5s (dc5 io b iauy98snmmx3cal 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.ui( md5 x8si30nsaiy 5o0tbc3mtl 99 y 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 convertkjr6si wbg;ev9 m2 6 tqn)c64n+xv 3xt a candy bar directly into work, how high could an 82-kg man climb a ladin+9; 2v)6 x g4mkxscqnbvj6t6etr 3wder 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 ai0mntqzgs i 3j3j:l 7* t0elp9t an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom sc4 0-fjzsd*n* s1zgpr)* lqj)lvpg1 yoale, the spring inside the scale compresses 0.60 mm, and it tells d*l-lyv*1fo*q szgjn0))jp4p g1 sr zyou your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs jd+ 2uei6l6wcat 5m/s grabs a rope, and swings out over a lake (Fig. 6–45)l2+dcu6ij 6ew. 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 cli:sold lcpy;to l2 3, 2te8bia*mbs a vertical distance of 5.0 m in 9.0 s. What minimum power o2ysab3: o ;2t tdecl 8*,oliplutput was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. W8e,tpa jbaq11ater is pumped by reversible turbine pumps from a low to a high reservoirb ,a1j18taqep. 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 id*f qvnn 5+4 ntbfb vcaad:*)(jv/t(stiffness constant k is cut in half. What is the spring stiffness const +jbt(ann4*vv/5 ba*)cf ivqf(t n:d dant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 1; mqflwy;.q t g-*ou5)j 8hfhc.b gyrm up 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 acc7.imtikhvt(6a q0zd p43r lhx1yf7d4 elerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglec f7q i7 lz(.yathtvdhx 64r01 43imkpdt frictional losses.    s

  In a common test for cardiac function (the “stress test”), th3zkxnke7m o 2.e patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required froek3 kmnxz.o27 m 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 verticallytyqk6t s6 6ab7 upward a distance of 500 m, what was its velocity aq6kt676bsty 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 water wheel from a heightr;0 k:qs2:jn*d sg5hjr1ga m*n*zg9ek o*ukh of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power ou;*h* 2zk gqhgskgnkuo r:a jm: 1ej5d **0rns9tput?    W
(b) What is the speed of the water as it hits the wheel?    m/s