In what ways is the word “work” as used in everyday language the same aa;wdek+4; kqr s that defined in physics? In what ways is it difq+ae;kdkw4 r; ferent? Give examples of both.

Can a centripetal force evnb + krrr1ito yszqhrf;x4eg6 * l1(26er do work on an object? Explain.

Can the normal force on anq en(l lyr7g4r2t,ak/ object ever do work? Explain.

A woman swimming upstream is not movimy e lnb)d 1is9a6t43;jqnbii:ujp 81 ng with respect to the shore. Is she doing any work? If she stops swimming and mer4ielj6ay)1 q1dnmiib8t n;9 bpu3:s jely floats, is work done on her?

Is the work done by kinetic fr av oaq83sdj4i.-z 5zhiction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under tj54sa vd.3h8-qz o iazhem.]

Why is it tiring to push hard against a solid wall even thvpm3b7*wp7fui3i+ ku ough you are doing no workv3+p w 7ik mu*iubp37f?

You have two springs that are identical except that spring l is stiffjgb23.k :ozkyk(r j)j er than spr.koyg2 3 (jj:k)rbjk zing 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 consta3 wdi :7;oojetnt horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled a dis7o i;de:j o3wttance $d$ 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 gravw* 89fss5hdcr sx7g*k klwn (4itational potential energy change when you jump as high as you cas48wrc*7ks n 5lh(d9k*swgxf n?

In Fig. 6–31, water balloons are tossed from the roof of a building, all wit*ailivm z5+0cmj5k4vh the same speed but with different launch angles. Wha5v5c mm*vi04k zijl+ich one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest pog9/ vg1nqnca;bxs h4(int 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 velocitybg/4 sh(xn1a vnc9;g q of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright 7t d .aw,unrl*on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the lwaurl*7td ,n .aw of conservation of energy.

A bowling ball is hung from t hd*y gj7h-mcdro -aq b*(-t*ohe ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against hisar(d--mdgqhyo*- jt c*h7ob * nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational poten8b ai87rk-s 5ckp z0rhtial energy when water at the top of a waterfall fall hrakp0c78-k8sribz5 s to the pool below?

Describe the energy transformations when a child hops around on a-aaap m(v o-4y tz9p0d pogo stick.

Describe the energy transformations that take place whe(bni f qm8)ej3n a skier starts skiing down a hill, but after a time is brought to rest by striki8b eqi3fn j)(mng a snowdrift.

A child on a sled (tx *v2a ge5i7w3r q3iygo8n9vq otal 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 angl2iqarqw5 8gv3o v973 iyge nx*e of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to stri 63z2sa djjub0do8 7ep over a fallen log in their path rather than stepping on topzr7o jid28sj6 0ua3b d and jumping down on the other side. Explain.

Two identical arrows, one w x8pz2jby2e: 7o5bjr with twice the speed of the other, are fired into a bale of hay. Assuming the hay exep 7xejbwr25z:b o8 y2jrts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple l60f kpqrml7(+db +;v:o fmk aswinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfadffm+(:vk 6qlp7 abr+ ; okm0lther clock has to be wound up.

When a “superball” is dropped, can it rebound tocqwck:q ) n3+(agw o.m a height greater than its original heightqm)q3cw(w+o.a gc: n k? Explain.

Suppose you lift a suitcase from the floor to a table.nf frx0e ql41pml16wj-; g gj/i is)l+ The work you do on the suitcase depends on which of the followingl4 / q0rw; jsni1ggl 6)xf+-f1jmpie l: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than th2jf jof/ ggfd44 /vo3je work.

Why is it easier to cbj3t*p jb sw2 h6psw2)limb a mountain via a zigzag trail than to climb straight up?p23bpswj2h6 jsbt w) *

Recall from Chapter 4, Example 4–14, that you can use a pulle/ o6i w5r f)qve9m;vy*)d5zqnyhjc 0a y and ropes to decrease the forc; a *)j5cviqfyme)rd09 w5voqh ny6z/e needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force w5kvbe 1 :z0) t0dmddwnhen a 265-kg pile driver falls 2.80nd1w0vz) tddem :b k50 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 23uu yymyp+k:a:n :w.4imkmf5mw5 +ia 0.0 m high. How much work is require 3:pfyin:kaw++m4mim .yak5:mw5yu ud?    J

  A 1300-N crate rests on the f+/:vmnb l rzp ;vpr 1gvq/:2hdloor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a fricti/bmvr :pn1v /+hrd;z2gl qp v:on force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did/ p o5w-x 7jlyf/ (mq sjysgq)w7q+q0u the movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective cm/s x)sq /o-yq+u5w0qp(l7f gw yqjj 7oefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated fci85;zaw;b*xls1 cg by a force across a floor at a rate of for 7.0 s. Fizg ;i81* a ;cwx5csblfnd the net work done on the box.   J

  Eight books, each 4.3 cm thick with y6v3u r 7.bv mm/5wqdbmass 1.7 kg, lie flat on a table. How much wo / ub63r dvw5m.7bmvqyrk is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we might nokan0kq bvy480s6) lhkt otherwise be able to liff. S0 qvkk4 8 byks6han)l0how 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° incg*,l4 uh-vu ,mjx,:awh0x7yc ) lw nliline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Caluxlw-,0,g*a mhw4il x7lncujh ), vy:culate:
(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:k1swcp)0oxh8v jogdn6 j.3h M an acceleration of 0.10 g up16 whh8:px3 )oj0vs knocg.dj ward.    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 o7z, -udlhs.hy(4g65eu qxp ndistance 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, ap1n (8l uqzk u1.vs6yocting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10 ms8 u p6y(vl.ukn11 qzo    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 aceq.lm(c8h m+exmj /*euj 13*6vbpnikts 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, w8zg v 09pqso )/ft+hikith 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 incrng3ua7a;9 v nbeased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an electr 01 e1q*whx7dhpb z2bdon $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 j)lc:ys,.b. qpy cnw)6(nfnd 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 string exerts kycnnglmm 1 igt v0**;r 6,etbz,:a0kan average force of 110 N on the arrow over a distance of 78 cm. What is thk,i1*gtc: yl;bt ezn mn0mrga vk*6,0e speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s movesw5ywo 98 7kkhl d/zh1o a fielder’s glove backward 25 cm when the ball is caught. Wzwdokh 1yh/97 58ko lwhat was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what fs+ximt2jmi*:e x;p 8bactor will its minimum braking distance be increased, assuming all else is the same? Ignore the di:2s; x m8+pe tj*xmbiriver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skidqdfar42s- er9 (3y gez mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinety- de9r(qga4f 3e2szr ic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reacx6 )o/6pa:kaj;qbk xh *qert)hes the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitche: tpqk r*j k6q)6h/b)aoax;xer is about 15 m.    N

  How high will a 1.85-kg rock go if tytmb:)fo fd2q1co)o; 7 byn9cxf r//dhrown straight up by someone who does 80.0 J of work on it? Neglect air resistance. /q;9fb)fo2)o t 71xmyd:ybcfco ndr /    m

  A 285-kg load is lift/aob4p t 1pu0j+-k wfr0ueok*ed 22.0 m vertically with an acceleration by a single cable. Dewu1-fae*pjp/4ob otur 0+kk 0termine
(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 stiffnesst9f(t9l0ztka( 8r h.m x5eic q constant, k, of 440N/m How much must this spring b9 tl ttiq8c .kf(r0m(9hea5xze stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m highpsloy,m n 7 yj:hmg*s,e0s :t/er. What is the change in ns*sy/:h : tmpm,,jgso0y7le potential energy?    J

  By how much does the gravitational potential energy of a 64-kg poloik -bgr,u: j.e vaulter change if his center of mass rises about 4.0 m during the juj-:,ukb ogr .imp?    J

  A 1200-kg car rolling on a horizontal surface hpx,n 2xf +p (f1mikhi5as speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of12hmxk piipff(+,5n x 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2 go,:subgxku53i ej,s39va*f. nvko7 .10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relative .sg ,u7uboai k*sj3f:voe3k9 vx,n 5gto
(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 1600rocziut) 1.5v-ttbg0 m and climbs to the top of a 3300-m peak. b0 1itz t)o5-rctvg u.
(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. Tqlj :f7ro6c+h he end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of:6+7j hf orlqc the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.net1/n.d8di6 sqw; f3kk k,tz3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward?nkq fe;d,i w6sd t3zkt1nk 8/.    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a fri yru4x 1;qeadmuv:fbj8e-x:w na3g (,ctionless 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 shovex12 /fpwi*q lj) c5verr b2ph) up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’z2la;g3j nrg;8 ake)zs kinetic 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 mass ;ln ;z3eaj)8a kgzg2r 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 toa v )occ.),vge9x4rb pp of a platform with a spevxacog 9.)re4c,pv b)ed 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 mass5pzfni1+ v;ev t3s wl9), 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 b+1 tivz3 vwlpsn5 9;feall 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 loo ,ala3r3 xf0m l4bbs2jped track shown in Fig. 6–39. If the sl4b0ja mra x2b3 3,flblock 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 isv. zed3 g;5p jz2bn8tc attached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given p 25.z j3gbdt8 e;vzcnan 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 tied to a bungee cord wh5jkr6o2 l mec r(,ry-fn.dq3vose unstretched length is 12 m, r,efrj(25yl-qvmd k.con 36r and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to poinnh5b/yfb iq-11-o wqeka.q 5kvro 7k8t 1 where it is released from k7o1k/n-.q y8f51h qovek- bb5irqawrest. 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 agj /m::jg7knc: y*o1hlvd 3cmn 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 spring to be plv2kd1d rk;()zu snb-qn ,+d1da bh-wh aced at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when dq kswb)v-1u ;b2r,z1a+dd hnndk h(-brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8 nhepbf)7+ cfb.+ pr)d$^{\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 np/szb1 l. ,nskg and traveling 95km/h in opposite directionln b1 .p,z/ssns, collide 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 th:m-i/s21mrk 49 uhfiuq zzs i,e bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in t-fi1,hz4i q9usku/2 srim z :mhis process?    J

  A ski starts from rest and slides down a 229 1 anr6i0o ofr) z(q,tjia3hm $^{\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 ddyy z*q;t3 it)k/o/b 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 tob(uf vma xo4)*x8et a5 a height of 1.5 m. 4a(e*f8xm5vu )atbxo
(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, iyv*6u5cju-y i s pulled across a floor with a constant horizontal foy56 c-*vij uyurce 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 coaster in Fig. 6–41 passes point 1 with a spe 9i00*hopoc peed of If the average force of friction is equal to one-fifth of its w* 0i cooppe0h9eight, 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 steado8w./-kyoo5t+3 wcm s kzom-h y 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 ver.k3 1v8tlfpdzy light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when 8lkvtz1dp. f 3compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal(y2q he7h rp7s spring, Fig. 6–40. The block can slide along a tabq7h2y7rphs e(le where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the e; 9s vgf6z yiz2ru-z9space 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 wouldyu9i69g;z-2 vzszre f 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 pi4 cwm) 6 *q;nz* b vjehx6b38r0/fpih w8midqdano to a sixth-story window 16.0 4h dvcwxz8mq*fn/*6hqre)i;wi d 803b6mjpbm above?    s

  If a car generates 18 hp when tr ,ntk , kyq5ftnt4wi*1aveling at a steady 88km/h what must be the average forc,tki1ttn kwf*q y54 ,ne exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s +fi)5u t0z.*bvo ekd t,vqyw1. What is the average power uqbif0v,z.)5*+yo1 w vt ektddelivered by the engine?$\approx$    hp

  (a) Show that one Britigm5 * a(cdii8- d up7s0tcx/ /5mnkqr rwoe-h5sh 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-houilkz :;+ov +ugdl:.r*gb g 1 x4fvq/xqudzs) 7rs.”
(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 thats ig6vykxa0xq3: r +6j 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 c3x irqj6:vy sag+0xk6ar traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp) x/2b+.kdi8qndjwn -sayxn9 motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion dfru mx7oy *asf:/, .gtakes 1.5 s, what avera7/sm:x*fryug d, . oafge power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. Wum o4,-7pt8du-fgh* (,)p q kgwknfekhat output rating (watts) should the pump motortfeop 4k gnkwh* )mk7, 8(fu -pu-gdq, have?    W

  During a workout, the football players /jd.k71 ..mnsff(aotio,gz m at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and incl/ ,a.mi.(f 1om ntzgo.j sdk7fined 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 l1ya2,teog zz)g 0n33f b8phg 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 f7x t8yj0t,ztz(0vw(kql nr8 hill can it climb at a constant speeytvz ( 0k8zqn87(0w f,ljrt xtd of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor havc/jz;qruuntz l3/p)n hn)ajuc: 7 ,-ie to be able to drag a 310-kg box along aza )p;7q3u ntclcznu /j: jr- hiu,n)/ level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a jy93k o3y2npoqo4 ea4bm 92zs8 lgx/m7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that are desigsq/phkdydtp(c ki0 12y 6/2pyned 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, / qd yk(ihpy p2sdk21 c6yp0/twhat 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 cmzvzb 2 h2h :d:tl)ee1q off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to t:zbe22hz d:l1 ev)qh 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. 8 5wt3buoast4 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 minb 3 o54ut8swatimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track showd:q: yvqn(u56pu cn *iqnpf6/a(ku/ xn in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of radius r. uq(k*x :py an/6vq pqd:/unn( 6i5fuc
(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 afte):il4p*5v (bym 0zrkymy2g 6demu, nrr jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity d4mby(um )2: irg0myzyev 5nr *pkl6,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 horizontawpj 9bu xr.7l p6-sdy3l cord of length L whose other end is fixed (Fiyxw76pl93j-purb . dsg. 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 6b.kr 5 uf4erbj6n)uu the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300b6ure ku)4b .u5j6nrf 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 whenznw lmr2mhi sgebb9y:6:;od (9s ,c:u a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,0tc h,qc6y) ,7w huok/h00 people per hour. If the average lift ca coh7w,6c qh, ukyh)t/rries 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 and8 9fg mnv + ) qxck dis7+v/sxitz9klo00a7k)c falls vertically 81 m before striking the turbine blade)/i09k ak+t8x)g0lfnsvziqm7s7o+ 9cvdx c ks. 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 vertical loop (Fig. 6–44), the dv:n,wr4:4 e8+ysjxwi miy di.ifference in your apparent weight at the top of, 8ni4+s yx.:jdryi:i 4 wwevm 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, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy brz ycf--ug 5pw)yj 8w,ar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000g-wu fc,)w yjzp8 r-y5kJ)    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 a1unh)e- oh2cot 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 scale, the spring inside the scale 2m(t3y*rm yor:4fhw lcompresses 0.60 mm, and it tells you your weig 4m o*r3m wt2yh:y(flrht 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 at 5m/s grabs a rope, and swings out over a l;s8 4am eb(o*k lox9clake (Fig. 6–45). He releases the rope when his velocim* b8e(9slxl4 ck oao;ty 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 m i;d 2c.tneyyk ;htjk 1l)-a nq/iht.4sn 9.0 s. What minimum power output was used to accomplish t;qes)t4y.aj y /- cni2thlk;t.1kdnh his feat?    W

  Some electric-power companies use water to store energy. Wakw pyvri; tatc.p816z yr-2,t exj ,w(ter is pumped by reverr pt jay,,.c8w1kr zw vy-pi(xtet ;62sible 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 in ha mrqnib;k59mi( tu8/r lf. What is the spring stiffrkm8(;bniqrti/ 9u5 mness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roug4g9on tr* mar9:; tqklh 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 toqd1 p57;dk gah 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/hg 5p hd7a;k1dq Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pate 6q4, mwap3kv. vtuq3jclw/ vk)w16uient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg m31)6a v/4kw. wqc qveku3jutpw6 ,lvpatient 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 rockc- nvfyl0u;;bnu9 e2 y vertically upward a distance of 500 m, what was its velocity 20;nve- u9ubf c;yy lnwhen 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 95kg/s (a)jn-rtig16i)xuv s /hs :4x+ry If this water wheel is set up to provide electricity output, what is g tjruv-nr xs+x4: iiy/6s)h1 its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s