In what ways is the word “worke 6878 0c pw+jsf8nwqm8 bbvr,s1qulk” as used in everyday language the same as that defined in physics? Ipq8ju7,q s+kbs1lbw8em6cw r 8fnv 8 0n what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object r2y49tlv)wnkm gx52m? Explain.

Can the normal force on an ob w pcl9obr.xt ,t7xf):ject ever do work? Explain.

A woman swimming upstream irtg ,/ bguj6)+j6o wpxs not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on hwb j+x)6go/t, p6jgurer?

Is the work done by kinetic friction forces always negative? .q p7lw fy1k8g[Hint: Consider what happens to the dishes when you pull a 7wplgf1 kqy8. tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though gst09moi6p1 94*mf5 kaap rryyou are doing no wopap ima * mk69gf45tr oyr10s9rk?

You have two springs that are identical except that spring l is 1 iz-0to88bm wigovn7stiffer than spring 2 i17 iv-zn088gb mow to$(k_1>k_2).$ 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 fd))tp hspho42orce on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þp4 )sht hd2)pooint 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 doejlag ge1;,go: s your gravitational potential energy change when you jump as high as yo ;:,jgg 1ogleau can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with trb r6dms -a4 d*36zthqhe same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resista *da-t3b h66dqms4rrznce.

A pendulum is launched from a point that is a height h abo(m +igp)ic7 tlod1d ))zvb,r(w ;mu:f; p ipotve 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 second launch it is directed downward along the trajectory. Which launch will cause it to swing the imduw7()) p)ipod, 1(+fg;mirt:b vpotczl ; largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the sprddkt8 4g (z 0gmkaa/a,d3b i*-war +fming by pressing down with your hand and then release it, can the spring leave the table? Explaikdw3d 0i,g+kb raaa m a4gtd/*zfm(-8n, using the law of conservation of energy.

A bowling ball is hung from the ceilinluvnuc:0( ;oqg 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 supp ;lcoun:0(qv uosed to release the ball without pushing it. Why?

What happens to the gravitational potential energy whx y6c.npxc1+ zen water at the top of a watenc p+6zy1cx.xrfall falls to the pool below?

Describe the energy transformations when a child hops around on a j pa/02f9qm;z- euhqapogo stick.

Describe the energy transformations that take place when a skier starts skii/ju;u n w2v uk-47ocv; o mq :5-bg3fuqxz5olzng down a hill, but after a time is brought to rest5nwk2 4uqm:zq5;z-/oxjbvulug uv7 -;o 3cof by striking a snowdrift.

A child on a sled (total mass m) starts from rest at thmeu-b :5l1s cidg5j ceqna,od; h,17 je top of a hill of height h and slides down. Does the velocity at the bottom depend on :7hnj;m,-qsc ie1 bjc55u l,edg1odathe 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 path rather than ssdt*wt*p;z r ;/9jidu5 y9wsmtepping on sy;*pzrujs /di 9* dw;tw t95mtop and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are firedvk726tp6i3iryb x ni1 into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster ar xi vi2t76p1 3byikr6nrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (ah5das; uq.af3) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock hassqd faa5.3hu; to be wound up.

When a “superball” is dropped, can it rebound to a heigvkqb7hv h8o(;0p* astpl iq:; ht greater than its original height? hb* s:pq vpil v(;t70;hq k8aoExplain.

Suppose you lift a suitcase from the flo.d wfk6w l;7g4lc/aox or to a table. The work you do on the suitcase depends on which of the following: (a) whether you g6cfw/d o4. xlkl7a w;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 fsfst9z xf 45 7nsgf(d0or the power needed rather than the work.

Why is it easier to climb a mountamb 6ci, ijjva4l .d0ybe3.ms6in via a zigzag trail than to climb straight updi.sbb i.36vm ae6 jm0cj l,y4?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropesfp6kno05 au.y to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how u 5y0.fonpa6k much rope must be pulled up? Account for this, using energy concepts.

  How much work is done rk* .;(i ,+qlp vhmzqzby the gravitational force when a 265-kg pile driver falls 2(q* m,l; z vpz+.hirqk.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work q,xjpn96om a2 is requ 6j9xq,anop2mired?    J

  A 1300-N crate rests on the floor. How much work is required to move i+; fbi*nkvl:ajaj. 7q t at constant speed (a) 4.0 m along the floor against a:*qfn .a+jvb7lija ;k friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizonta2cxouh.a53r . tqo:stlly) pushing a 160-kg crate 10.3 m across ot2t.sr 3h:axq.5u oc a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a f2e ocb l+1.7ori6c gcm ;uk7ci2absf( loor at a rate of for 7.0 s. Find th2gi; b1r l7.c bas6oo7 (2fc cmeuci+ke net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie h)h inwnfc/b:c6ye+4 flat on a table. How much worn+w 6if bhn:ec/4y)hck is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-3514mp+bcns:o ti5 um8q can be used to liff objects we might not otherwise be able to liff. Show tm+1tb :4pmis8uoqc 5nhat 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 ken 5r -rd*q6tt9 jpgblei71:wy .pij /ept from accelerating by a man who is puj7yp:9 ntp.*d t1j-wr i6bl e/5igeq rshing 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 gby(h 9azq*y )give a helicopter of mass M an acceleration of 0.10 g upwar yyb(hg*z )a9qd.    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 -m 6tyu06o +p; pwqeyx w27*4zgnyqh vthe 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 Fig.5ghk.h dan1.f wj*/57lat rzp 6–37. Determine the work done by this force to move thf. 55hk/7*z grawtpn l1ha .dje object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particlelhqlj92m 8h)h 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, u6 3el 43agahjan oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is dou+ulnd8d 3u8ov+e8nmtgm j /6ubled, 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 stoz/vyv4 w.ji3 ap an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcarl+gndj xn s ain5e(74w q/:fq, traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a b1xdwywbk7t k5kh 0oae:o -oro5i( 7l9ow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of tbo1 k0o5rk9 y o(x7dit wlh-7ka:ow5ehe arrow as it leaves the bow?    m/s

  A baseball (m=140kg) tni5ia .+z s5v/h 1solwraveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted bywn.+ii1 ovh5z s/s la5 the ball on the glove?    N

If the speed of a car 4a5 tolxa)r9 d iu.d/gis increased by 50%, by what factor will its minimum braking distance be increased, assag /5d.airto ulx49d)uming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’m i4k-qu hz, d6fxl;r0s 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 car’s q4m0x f6hr-luikd;z, mass not matter?)    m/s

  A softball having a mass of 0.25 /*o5 pbg pd-w neuy3h1kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistan g d3uye/no1*hw5bp- pce 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 ifd 9o.nhymw, ynz7 o 0;b emm8/jz:5inx thrown straight up by someone who does 80.0 J of work on it? Neglect aib ndnoe m,5zmyn hm 8oyz;:/x790 wji.r resistance.    m

  A 285-kg load is lifted 22.0 m ve6l*8 l)-zuw9m xe0fb lhm;zk urtically with an acceleration by a single cable. Determinz uh)* b lxul 6fklmz9e08;mw-e
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m Hoolvugw kl0 1u+ 7zxf0pun6r x 7/s:0sjw much must this spring be stretched to/ g60kwulx lxrs0+jf7 uzpon0u s7v1: store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m highe mpvkjml +q-.g;os0e (r. What is the changemj.vlkmq ps (e+;go-0 in potential energy?    J

  By how much does the gravitational potential energy of a b*;ousirqn8 + mdkmdy0+ st34 64-kg pole vaulter change if his center of mass u+mq8dt*s no+m; i0s4b3dkyrrises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kmxq- o,n,9rzmm/h when it strikes a horizon9 , m,nr-qoxmztal coiled spring and is brought to rest in a distance of 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 2.20 m abo8o5, c ub;jh6c)rwe qgve the ground. Whatg6e w8obhu,c)crq j5; 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 6 xxv /dod n*a-;bst1- vvrl a47-vywuof a 3300-m peudv tn*bvwyl; /x 1osv r 6xv47ad--a-ak.
(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 hanguakakn9m e5 wl3-moope:q2.s f;7b6fs 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 n-o e57 9k3.uml6ofa2wmabfk s:;qp eof 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) cziv qn )6h3vap :(9uxand grabs a vine hanging vertically from a tall trev 9xu)qazp v(ch6:n3ie in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dowq 3d do t7raemgd.*r07n 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 frictpmr a:jibkvbq1.3 g93uuf7h+ ionless 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 enerymnrcfxf2 *9s9y* go+gy is transformed into gravitational potential energy without the aid of nc9* 9 syf*mgrfo 2x+ya 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 art(n x cc1gl(6jwuy+:oe ist jumps vertically upward from the top of a platform with a (c1yu gcx +(el 6o:wnjspeed 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 myid 23xsdf l(88s8ed dass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when releaseddds y(8 l382es8dixdf ?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m sli 7j0a bogle o0gbqh mq+3ha +hs3(bs5.des without friction along the looped track shown in Fig. 6–39. If the b .s33ha+l (ashh0bbgqqoejb0 5g+o 7mlock 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 stiffnessgra 3 n)/+trjs constant k), Fig. 6–40. The blockg r)3 a+tsjnr/ 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 brxfk57xqzgc. xb5/xw 1 idge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord,qk5z.x7 xf1 x5bx/wcg 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 drah1(m7y :trb nni0 nsq7gged up to point 1 where it is released: 7r17hymsn0btnn (i q from rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an anyy1w6 uh iz(y:gle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the botto4fw40yj ucqvg53 c4k jm of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mas4g04c45c3 w jvjku fqys of the elevator and passengers.

  A cyclist intends to cycle up a 3r 7h -dge01cam2qm4c r+nhgs 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 nf*x( q, v;oayand traveling 95km/h in opposite directions, collide head-on and come to rest. How much *a(yov,fqxn; thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hikmv( adfqvd. **jq9 r x:3gh(jj0e7e tgh and reaches the bottom with a speed of 2.2m/s How m3evr0 j qkt*:dv gd.(j9ej* fqam(h7xuch thermal energy due to friction was generated in this process?    J

  A ski starts from rest and sliewg3 4xn7j38d wggrc3des down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above t6nh.tqjs q)9f: u zy/zhe 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.miw +7mvjfu7,j5vka /*pjb s7 0 m, and it bounces back to a height of 1.5 m. *7uj+,f 5vaj /mip7bkm vw7sj
(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 floorxy v:k rv05*vh mma-m rd)y3v9 with a constant hordv5xkv9:v*3 arv)ryy hm 0m m-izontal force of 350 N. For the first 15 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 cokgk6v6:tkx:(z l 7 b2:npmmi85bcp wfaster in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with whakv7: b6:wm8t p5n 6(bkz :iklx2p fmcgt speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the fa + myb cpip8smw0)n:1oot 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 attaxva:ccq (o1*8 azcaon75d ik)elx ;k+ched to a very light horizontal 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 turning back. What is the coefficient of kinetic friction between the block and the tableq c;di8la*o cceak(a7kn z o)1:v5+xx?   

  A 280-g wood block is firmly attached to a very light horizontal spri g9mct0gw de re8:n.9bng, Fig. 6–40. The block can slide along a table whe8 m .9cwbdgt:eg0n9e rre the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider2qwtgvxkfa 4+u3 p c1c.;it;u” (mass of 980 kg including pilot) that was launcvcwgt; 4 ua1p.3kxuiq2+ cf ;thed 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 resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-story wi-ohm t7gli3fxke(- lu/q / 8ypndow 16.0 xu-l( k y /lpef/tgqh7o-m3i 8m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be29vtx (t tcso 4ca;)ct the average force exerted on the car due to friction a9a;(o xc ttst 4cv2)tcnd air resistance?    N

  A 1400-kg sports car accelerates f)5 hf 4lxj0bbjj ;g99hrdzab /rom rest to 95km/h in 7.4 s. What is the average power delivered by the en9bf9 bha0bxr 5zj)/ g 4hjd;ljgine?$\approx$    hp

  (a) Show that one Brit,jlhs :z jy5vu48oie 3ish 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 expressed in the form of “kilowatt-hours.u:z j.ajj ob/af r820q”
(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 6ph,r+vt/mktbqn2k yd r7 .b8 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 and hp) is needed to keep the car traveling at ab/+.qrd rn2,kbv7ytmph6 t 8 k constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h? re il:u 3bcgez39,ar3$a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this mqx (gqqompp:cdx -w8/ cxn.k; lk;)1wotion takes 1.5 s, wh;kg.w/w: 1 -)dqoqqc ;8kp lxcpxmx(nat average power was developed?$\approx$    W

  A pump is to lift 18.0 kf l1kw s9i7 c/g ,tna6cglc2f/g of water per minute through a height of 3.60 m. What output rating (watts) should the pump cfi7 ,nsc wcg/ ag/1ll2tk9f6motor have?    W

  During a workout, the football players at Stafqs g +3:x pi4-uwf)*qk4dw nfte U. ran up the stadium stairs in 66 s. The stairs are 140 m lonff4+q f-3wg4 kis*)pu:wqx nd g 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 akwf .: hy(i s0b,zyg;k 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 o .:; 1;qfzxxp2 fsad2yrbwm/mkr1 6kd utput of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forcexkbr; :s d2.xfykrfa/;1 wzqmpd12m 6 s add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box along z:ctd iqyixyk;j x)5 0e: 659h-igzgia level fl ihji g );cti509k:xxdy: 5-ig6ezqyzoor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down e1a9sxfst f*7w)xkh 6 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 tt/* h;rz i0827nvr*2jozr xzapf6af “5mi/h(8km/h) bumpers” 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 comn va8f*i/z 7tzjoax2 h*02r6rtpzf;rpression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm oqrjn /kbl3v y u9ljhm 6hc .6/tx-w.a6ff 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 holds 25 books, how much work is required to fill all the shelves, asy66-h kmlxb9anq6ujh..3j r v / /ltcwsuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owensj8rpfdun6d2(37 dp(hv1( mdw3 hqweu68py m b’s famous long 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 traveling at 6.5m/s at thp2euydvqw j d6h36df8 3rm (hp(pbu n8dm17w (e top of the arc?   m/s

  The block of mass m sliding without friction along the lkrpavq5 ,oxm4;wvui ag;g/ +7ooped track shown in Fig. 6–39 is to remain on the track at all times, even at the veryai v4g,ruw/xvp;+gm5q 7ok; a 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 3adptyff2 2a0zt y75 a/kgn n08t3mk/v70 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but s/v2t aakgyp d0zk3t f/t82y5mn a7fn0urvived 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 h1q5a qia6sry7m nmh :+orizontal cord of length L whose other end is fixed (Fig. 6–43ar5m qaisyh7:+n6q 1m).
(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 mount ,7l yqgr qin1+pn p-b:kir,5lain. The climb is made in 5.0 h starting at an-,p7in i,lrpk g :n5yqqrb +1l 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 ( :f*p2fvt goe920-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 Californixk ;(*fnrcvl*xb( e b)a claims that its lifts can move 47,000 people per hour. If the average lift carries people abou(kxvx *)b l(rn*c f;bet 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 lnx -sli8rl0t u nr9h ,f97ao/vertically 81 m before striking the turbine blades. Calculate7llr a,u rns0 nihflx-9o89/t
(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 ipnf88zf)nk2h k,fs4 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 — thatk8hf f,zn2n4) 8s pfki is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a cyo- v,i)nf v;oandy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bavfon;, yovi -)r (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward anjq/ n iv8 6ez/b:pwcrq56mlke8c6) lcgle 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, tqj*h)ugc ptto;1 3el 0he spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you ju1;)3qg t0tco*h j lpuemp on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs t7c5y5i cc r.rat 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velcc ryir.c7t55 ocity 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 y,4qy.nw8am4bv ss. :4 psc0;b 9zd qcdqqwo+a vertical distance of 5.0 m in 9.0 s. What minimum power outputdd; ys snqm+ap qww.94:z4vq,y. 8cq bs04bco was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water isxt:zl.fw v* )t*3 m xg2en6ost pumped by reversi e*nxlx6ttg*:3sof2v )z .mtwble turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut i3 v1l2oji /66stwj6 +i sdu dhhzj;nn3n half. What is the spring stiffness constant for each of the two resliwdh6dot/+3znjh;1jjsnv 26 6 uis3 ulting springs?   k

  A 6.0-kg block is pushed 8.0 m u( ud42a u)*tssj *nlkpp 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 acceleratejoar,elm ,-dxa,luard 6l*.k 4)x * do 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 neglect frictionall ol la.urxxd ,daa)*,,m* -oejr6dk4 losses.    s

  In a common test for cardiac function (the “stress test”)ru9ol: igr0;g, the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill :rgg;u0 orli9 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 uee y;-ob*hee7 pward a distance of 500 m, what we7hebeo ;-e*yas its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.0 m at a rate of 95/gnzx 9o8- vun l/m*cmkg/s (a) If this water wheel is set up to provide electrozc mugl8nv9n/*x /m-icity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s