In what ways is the word “work” as used in everyday yx+j13oms,) 8ndrxdm(d+yb r language the same as that defined in physics? In what ways is it differe d8+ybrmx+1 ymj)nd(dxrs 3,ont? Give examples of both.

Can a centripetal force ever do work on an object? Expla gmxk/z)cmb3 9m* fi3vin.

Can the normal force on an object ng kas/)je7w)szsruu5:r ;:b xb+w.c ever do work? Explain.

A woman swimming upstream is not moving etqvhll*wp ,g uy/b3 k-s *o -4dycd0.wu w;f.with respect to the shore. Is she doing any work? If she stops syd, .hbu e /0l.lw;q4s*cuk-vodgw-*tw3fp ywimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Cb -vjb jc4cb -.8cxxi)onsider what happens to the dishes when you pull a tablecloth out from under them8.c -jcxi4)b-j bbxcv.]

Why is it tiring to push hard against a solid wall even though you are dqju*;skr-m 6r oing no wo* ju;rmqk-6 rsrk?

You have two springs that are identical excl* cd w3zy:+glraw- +bept that spring l is stiffer than springr+zw*3daw-ly+bc : lg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slidj2a02 vs8 uenze on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it hase0nuzs2 a8 2vj 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 gravitational pot )gqsj anaqp/s wnm9: 20:cmr7ential energy change when you jump as high as you am2ag/c:90 r 7qjns :mspwq)ncan?

In Fig. 6–31, water balloons are tossed from the roof of a building,cm7l+0tu)bj4 q1, j9on zkep iodi;q ; all with the same speed but with different launch anj;qm d,+0ozice oqp; tbjnl1uk9 i74) gles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point th-og +d(i wmzutq5) 5imat is a height 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 second launch it is directed downward along the trajectory. Which launch will cause it to swing mi+)qgi5( dmtw z5 o-uthe largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spxpe6qjq .h6c3fp qb,)it 6s t)ring by pressing down with your hand and then release it, can the sh p bxq3)cep 6j.sqt tf),q6i6pring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from tz6/nbr ob;w p:he ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why 6nw;bo/b :prz?

What happens to the gravitational potey.t) hr1ij /v5v xm:, egeiv9bntial energy when water at the top of a waterfall falls to thmbi )vyv/5jv19 .:e h,xer gite pool below?

Describe the energy transformations when a child hops around on 1qk n* ,6:c ziz:lynmna pogo stick.

Describe the energy transformations that take place whe9e3ya5y ieuv, n a skier starts skiing down a hill, but after a time is brought to rest by striking a snowd35i, ey9avue yrift.

A child on a sled (total mass m) staa a4kpe 22b8wfrts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom dependkp8ba2w fea2 4 on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their sv*nfl e:3lgog) :;j/jp 8dvupath rather than stepping on top and jumping ve )fj go;ul3pv8/d:*j :l sgndown on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a b:az r b/,dj,t4:hsq.u igzf+ 7hmpt;a ale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much fazh ,t f z:b7a u.,:t4d+;h iarj/qgmpsrther than the slower arrow? Explain.

Analyze the motion ofx5o)g8xpcsn ( a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction xx8 ngcos5p()into account. Explain why a grandfather clock has to be wound up.

When a “superball” ig e mu;8y+ ys8bvr,4wfs dropped, can it rebound to a height greater than its original height? Expmyrfg8u 4vwesyb+; ,8lain.

Suppose you lift a suitcf5r+u/ 3kgst( opk5j gase from the floor to a table. The work you do on the suitcase depends on wg /u+ ko(3k5gs5fpjt rhich of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed raoqg92dr7m(u g0: vr syd 0emkap5go1 4ther than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straight2v mcbpq55 0zs upv50 bz cqm2s5p?

Recall from Chapter 4, Exagfkamnb dh 4:58x2;x io7,, +rjs .xspxig i5dmple 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the bxjsk;ixx8ipais+x5.4fd r nm,72 g5h,od :gload is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by (4*jyj x 3dezebtq6/hz*5 t tathe gravitational force when a 265-kg pile driver falls 2.80 m/5 jet *yj*d3axtz6ebzh4(tq?    J

  A 65.0-kg firefighter climbs a 5pwld,rrxlv a4 r/93gflight of stairs 20.0 m high. How much work is req d a/rl9r5 4lrxg3,vwpuired?    J

  A 1300-N crate rests on the floor. How much work3u qlr1y/x ek7 is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 N/3e7 uqxl1 yrk,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing 5 ,tzsjx;xfvslvb :51 a 160-kg crate 10.3 m across :fs15;z,v5x lxt b vsja 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 fl c9o7l0xd a5t7)be kufoor at a rate of for 7.0 s. Find the net work done on the box. 5tl7) a90cdb7xfoeu k   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How 74r.w 1pfoggd much work is require41w.gdpo 7rfg d to stack them one on top of another?    J

A lever such as that shown in Fig. 6- k32uzq s rvf)0620iywvhcmv+35 can be used to liff objects we might not otherwise be able to lk3vs2y h)fq 6+mri cu0wzvv02iff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from a gtc sh2ids(()ccelerating by a man who is pushing back os(ic)(st d2hgn 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 tos/*9d lwqc7/rgwde jt8c +yip)mb1y 0 give a helicopter of mass M an acceleration of 0.10 gi0y/j q wbdm1drl/ts+)gpey 9w7*c c8 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 isals .,2 )qfb8-+lsqit/re 2boy uwr2a 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 ywaoti8q+.x z4+ gz 6palong the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to mov a p8.+ziwoq6+tz4g yxe the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a parc9c3v7obz7n yticle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, withxel wg 8b45kefl*u b). 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 6*u l jkm z*t)oi-imf7fh,0 zkfactor 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 sz7 0 fb)*.rj ekxaej0gtop 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-kgcar traveling ,uuxytxy:vr,bo 3; m /r.hafqep79v* at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average forc 6pnvgf2u,wt 3nd qm34e of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it v64q u 2n ,wnt3f3pmdgleaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/f67yhp 0( ffc*d8tdpl s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by thl0 tc7 fdp8fp(6d* yhfe ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum +;,7w:t0+ m a-sherusuw ile3.tvbou braking distance be increased, assuming all else is the same? Ignore e73m-uo+twv s,;ietshr +auuw0b :l .the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car jz ,c;ah9ye:h3t dxqv+zr0 ix5+jft5’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.i5tr5x z0hax9qd+f3z ehjtj, :c y; +v 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 oo o 7hpu09ke;uf 0.25 kg is pitched at By the time it reaches the plate, it may havo0euuo97k ;hpe slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straw 4 i+f7/xslzz uyh 6ae(4gi;u1+yszaight up by someone who does 80.0 J of work on it? Neglect air resz+iys/iezuu1s g4 y;l7aa (+f6 4xhz wistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single i3lldcn/ cf,6cable. Ded /ccf 3,il6lntermine
(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 sto8ig2t0w72bx6 kciboez i 1x4 iffness constant, k, of 440N/m How much must this spring be stretched to store 25 Jtc oii1iobe2zg27xx8 k4 b6w0 of potential energy?    m

  A 7.0-kg monkey swings from one branch to anot 7p.h9nijwy 4 ir:j2na ,8nyxjher 1.2 m higher. What is the changexj.wr,9i2j 8 i njpnyh7:a n4y in potential energy?    J

  By how much does the gravitational potentialgx8 *h/kwhl yvj0 ,m+ldvr: o4 energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m d0*k,gh vm4djl 8r+/vylwho :xuring the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = :ijsr7px bs e6+*)ln x65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.6s7xin x)* b:e+jlr sp2 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 : eky .*2 :ffvv,aeqzim above the ground. Whatkfvf2v :ie,*z e:y aq. 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 top0oxuttmpq+c4x,oo vj u 3x4 gk,.*p.d of a 3300-m o4c, x0m.g4 qu ttxxu.d,3*jo +ovkpp peak.
(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 the bs wy gdn1:,p3l; efk825dcqbspring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler medbbfsw1d gk3pc,5n:; 2q yl8arks?    cm

  Jane, looking for Tarzan, is runnje ghw jzx47c+sqv*7nhg( n q/ k+um14ing at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upwaghcs 4+zjgm1 4n(vequ h/n7j w*q7kx+rd?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, start(lfhkiowakdg o 2:e0wp9m( 3) ing 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 lh:g ;.+bwzzl:t o ry; lv.+mv28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gra46pu t x wob ,lpnl4yv,)11 djf7;cvjbvitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lu44p7l6cj x1ylo j, tdnp 1);,bvbw fvift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the e;q tp-0dx/.iyr. h67jcr h7ydk +zlttop of a platform with a speed of 5.0z.0+ l rdxt7qp hj7.y ;t-yhr6k/cied 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 (ignw0.(leikm7osk 1r by0 ore its mass), 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-k7 .k bo0rw01 sim(elkyg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction alox 1f ezzeg843lng the looped track shown in Fig. 6–39. If the bloleez3f z81g x4ck 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 tiuw2-)0wc6xj+ tbklkg-q q9(spring stiffness constant k), Fig. 6–40. The block iskxw t-+jgb-9qt)uk i2 lw06 qc 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 brivj,q0ut dpb))a fu.b5qr+ /mi dge. 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, assuming Hook +)0rvp)u5 atb,m/f.u qj bqide’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 i .rzk6vlb(*ofs dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at point b6fkvl(.rz*os
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 aq ,ht8 )o) *s+v+auu,wihs pnqngle 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 designipkt rp)2x f,t72/3zkz(afh bung a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of 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 to32p7 f( 2fazt)x ubhzrpk,/ kttal mass of the elevator and passengers.

  A cyclist intends to cycle up d8opcg-o1/)2erhtc v hzc .w/a 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 kgj1vs, *o.p lcucsg0;vvi;*ub and traveling 95km/h in opposite directions, collide head-on and come to res0ui*v; sv,jv1;*.lb cs opgcut. 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 rea((j12kxpl/bu1guig r,qt3x7 oqrzj n3coq/ 9ches the bottom with a speed of 2.2m/s How jc/9u xx(ul ,(23o7qqrngbogti/ zkjr 1 3p1qmuch thermal energy due to friction was generated in this process?    J

  A ski starts from rest andlkt( /ywc(b3z slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree qg:(3w*h h4s npzk,t-wr kzn7by16ki 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height obv*kz4pc43- 6izph ax f 2.0 m, and it bounces back to a height of 1.5 ma3* 4iph4pk6 vzzxbc-.
(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 gpa2d98uwacr z tn65 6rest, is pulled across a floor with a constant horizontal force of 350 N.96pzwatr 8ncdg6 5au 2 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 speed ;a-dbkg :xed 8of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The disb:ged 8xa;-d ktance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upu 0gvq r..mle;ward 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 firmlh2;g -lfs6rjby attached 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 coeffics lg6f2- brh;jient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly atoz9z5yd; g25 ibpr y,ttached to a very 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 comp oz gi2bd,t5zry 9y5;presses 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 fq -kxv t1cxg9h 9cej8w02k80agk9vy por the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at t0 c2 pka8g0 xvy-8j qv1kwe9 cghk99x500km/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 y3n j, eajkbyk-;,4azlift a 315-kg piano to a sixth-story windoweka- ja k, ;y,zbnyj34 16.0 m above?    s

  If a car generates 18 hp when traveling at,xtyib:,fae4r 1lw8 t a steady 88km/h what must be the average force exerted on the car due to friction and air reslx1ie8,r tty: a ,4fwbistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h ims1o2f 0lj rk5n 7.4 s. What is the avera5l1 fj02ms orkge power delivered by the engine?$\approx$    hp

  (a) Show that one British horf5 ml 0ysk w;z.(ov9bhsepower$ \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 oft / l qsn9s7ztd8sj8h4a7kvvq4 en expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in abou wz.1r89uaqn xt 6.0 s on tzxnw.8r91 uaq he level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do 8 9jabw8suh1y 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 4uxc2fx fcv; 3k :u(mztakes 1.5 s, what average power (fc;xv 2 zkm3 c4ufu:xwas developed?$\approx$    W

  A pump is to lift 18.0 kg of water perwq0. ,gwva+aikul+)y c8e b*z minute through a height of 3.60 m. What output rating (watts) should the pump motor huk80a.l +e+ ac ywzgbi*)vw,qave?    W

  During a workout, the football players at State U. ran up the sta)a78. 3:t+ wq mnslow-1e /pdlnx xxiwdium stairs in 66 s. The stairs are 140 m long and incl:px io7+ n1n8e s)-3mwqxx/tww dl.alined 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 cyclo)h)b sw;tl d 50qcsm7ist 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 h)4 r :i7,*zk* c12dejpujz cqkxn9w aap. How steep a hill can it climb at a constant speed of 75km/h if the frictional forczerc1qx *da*jk zp42 ck 7i:uajn,9 )wes add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 3b1 1c2f;n gxea10-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45?xca1;gf2 e1nb    hp

  A bicyclist coasts down a 7(* vi;t4xxo fow0 kn*h.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 car0(j6. g)lsuhgu 6rc wze.h)rn s have built “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 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 thewuh)h)jgr(gc nlzu6sr06.. e 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 g/:euzyg3 1h vdld4 )goff the ground, and the remaining four shelves are each spaced 3e)ddzg:gy u/3h4lv g 10.0 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, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’ezij)*i(i: uxbm+ a 6ctlij85s 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 xumtci)a8i l j+5*e:zii 6j (bneed 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 lofj8gsbf; f.f b.o )2kaoped track shown in Fig. 6–39 )fsb;.kf2ba8f .j gofis to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircrant7t44*p x8 ym4sog :nmeqp :nft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming ths :m: n*xq t4g4onm4pyptne78 e 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 horizoeha . r:oz, 5x.lklfvm85s +pental cord of length L whose other end is fixed (Fig.o5kples:e,xrla8+vzh .m f5. 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 toymb5/ietdf)ou 582 5 dwpaf e3 the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation o5bo5wd53 d a8my/fu)t ip fee2f 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 whec5z nlhhq,0ut2ft5 o8n 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 47,000 per7t w+d v 9v3f9rhm2people per hour. If the average lift carries people about 200 m (vertically) mvrp3fw+ 2de9v7 9r thhigher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s anda7ke r);gc e5h falls vertically 81 m before striking the turbine blade57ega rch k;)es. 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 circu+ledo7 v9s7hxlar vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop a9sve+ 7oxhd l7nd 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 conveidfv99l.u+ e;-uhw l frt a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fh9vlilu- e 9u d+wff;.ueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at l3f8w5 caw 0i7ft,g uhan 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 compresse w)24v9ya :6amocmf ie cbrc;4s 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of:4 ;c9vecyc4 mr2 aamfo)6iwb 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 over4h:-x 1iikpvdp h jrq+)h*zne (4z.lh a lake (Fig. 6–45). He releases the rope when his velocityd- hi(zxrnzjlpi+ q .h4)v h1*e4kph: 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 in 9.0 sf3n(dm j6p 0* 6qm4 -dz64bjq pwkvfnv. What minimum power output was used to accomplishw-pqj66v* q(f0f4kdzm3j d6b nnpv4m this feat?    W

  Some electric-power companies use water to stoah,z q506 5a+hg)ctjpkck. eare energy. Water is pumped by reversible turbine pumps frhkta)+.,jk c gah05q56cz aepom 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 half. What is the sprin dsc(-(ahgbr; (h.txj g stiffness cogtha( (.jsbrh;dx c-( nstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8a1tupy/atkkm054bl2 s vmx. 8.0 m 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 accelerknu6 5m 6(*,sw bi;8rhghpzp kate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h ku5s6*g k8;r wppnh,b miz(6hAssume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (t,7 (xit:btfg xhe “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the powb,tt:gxi fx (7er required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a dista(- iz0 g(qwfqince of 500 m, what was its velocity when it left the vo q0qi-ziw (fg(lcano? $\approx$    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 wataww*y: q;6jnrer wheel from a height 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 maxj n:6w*;q ywarimum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s