In what ways is the whdfoc )tc:h2u 9wu4 1e)he2 ivord “work” as used in everyday language the same as that defined in physics? In what ways is it:4hi e )ut c)ovcdhe92w2f1hu different? Give examples of both.

Can a centripetal forceclb1h +5 r0 yc mfskauc.xg5,3 ever do work on an object? Explain.

Can the normal force on an object ever jq ;qwjlp5 +*rdo work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is s81 9i tzefb,jqhe doing any work? If she stops swimming and merely floats, is wetf8j i1qb9 ,zork done on her?

Is the work done by kinetic friction forces always negative?fn*j eh)ha63k [Hint: Consider what happens to the dishes when you pull a tablecloth out j6khf e)an3h*from under them.]

Why is it tiring to push hard agaq4f c :qt,.ob raumd5:g2u id)inst a solid wall even though you are doing no work54:uf q o,cgq2 )dtda rmb:i.u?

You have two springs that are identical except tha;5+s2heyxtl62 vkrpq-ffy9 j sx4aa. t spring l is stiffer than sprin jhyq5+4 afkr-x2ps2y9v e 6flxs.at;g 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 horizon t-(,akejol u8tal 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 tiekja (,8u-lotme it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change whev65gcco(n )r pn you jump c(6pgv nr5o)c as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with :; *ltj89 3qzho3xmnwo5ctsd,*rr5 snsp,x athe same speed but with different lnl m5s9sx3jr8q d wos,*;cr:,5xz* t3ontaph aunch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h abovebm*v;+dvicqf g4z9s 5 its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial sp9cs;5g4if*vz +d m bqveed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on 7wy (lcg-t ri6dhs.vi own h2; qw/),sa table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, snd7iq h/.;cghils6 (w v,w2 -o) trwyusing the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–ef j(g 92abbngh:y)wj8 59wgb33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed towwjbh9ega:)g 2fg9jny8b(5b release the ball without pushing it. Why?

What happens to the gravitational potential energy wey6f tc651 ytfhen water at the top of a waterfaf6ftcet yy 165ll falls to the pool below?

Describe the energy transformkb+dku0gq pmid k5uq,(3p0o6ations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiinb (ebtv5:n aju6(djt1g down a hill, but after a time is brought to rej5tb:jbt 16u(vdean (st by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the t6i ,: gwe y9dj.b2whodop of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icyhg d.wd2 ow,:e96bjyi and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step overx .t+ *e8m7 i:hhypfbx a fallen log in their path rather than stepping on ttiye7 + b*xh.h:fxp8 mop and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, a9zt tgwx5g/z -re fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, tzxw-z5/t g9 tghe faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms0v f)m/pplkzm4r*;r h of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clocklrf4/v ) m k0*ppzm;rh has to be wound up.

When a “superball” is dropped, can it rebound to adywvboba h b )86eo5tx) r;)v3i.db )w height greater than its original height? rtav3 x))v wwbybddo)o h586b)ei.b;Explain.

Suppose you lift a suitcase from the floor to a table. The work b.)oiv27bo dz l0cev2 you do on the suitcase depends on which of the following: (a) e v22ldzvob b.7i )o0cwhether 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 tczhuv3dico/z g u),0r ph6ct*sr - t*6he work.

Why is it easier to climb a mountain via +, 17 ,mxbfytshvx hdd69 8p,uyup-b6 ahqu*ua zigzag trail than to climb straight ubu tdx,udu- qu7h ph 8*fv6xshy1 ,6b9,ya+ pmp?

Recall from Chapter 4, Example 4–14, that you can kk)wirh,+nmr +r2c2 s use a pulley and ropes to decrease the force needed to raise a heavy load (see w+m )i sk+n2rc,2rrh kFig. 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 whl t g4vqf4z.jc l4.p-uoj6 hz/en a 265-kg pile driver falls 24v cgzfluj4. - /6p 4.zthljqo.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. H) b 7-z6zdcfgwzl (3a6.y hjwuow much work is required? w)g. za6z3c6fz w-yj d7(hbul    J

  A 1300-N crate rests on the floor. How much work is required to molddyo 1ul. z7 x.x)xr5ve it at constant speed (a) 4.0 m along the floor against a .xu5lx )d z1odl.y7x rfriction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horc advlv2t*0r13g d(g(k buog29b;gpgizontally) pushing a 160-kg crate 10.3 m across a rough fg0 3vrb2cg*9 (pd o 2ggg;batlv( 1udkloor 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 floor at a rate of for ach;;xr66ydk) a yasij6+zm/ 7.0 s. Find the net work done a xkiy6/ja ;aymh; )s r6d6+czon the box.   J

  Eight books, each 4.3 cm thick with mass m-.fe9bfb.u z1.7 kg, lie flat on a table. How much work is required to stacm9 -.fe ufzbb.k them one on top of another?    J

A lever such as that shown in Fig. 6-pd;.rk j0y 8aohn h6h635 can be used to liff objects we might not otherwise be able to liff.n;y8phr 6h. ojh06ka d 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° inc/ rvd m 13ifg hwvyu7(x7r-hwv.h+8ay line 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. Calculate: d -y+v.ur8y w 37hmhfi 1vxv7g/a(rwh
(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 :epq8gp of etvb-b:5. M an acceleration of 0.10f.:pgo :8tq-e 5vpeb b g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance afwtys l1-cj q- y)oi-/xis 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 q/mc4 vne 1:kfaxis, varies as shown in Fig. 6–37. Detc kf 4qenv1m/:ermine the work done by this force to move 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 particle acts in tx0k;hsp;fpn 8r) uh( og m,7zhhe $+x$ 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, with mass xp /x6z3ete-jof $5.31\times10^{-26}$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 incpo5 0vgp ilqi62;sx2: lmoob3 reased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stopz*rkk 6i.j* r6(ltk nn 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 at 105km/h?mjc gu/l 55-wns4ec .c$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110 2 0fks)nt5yaj1o8lqt N jaos58 q1ttl2nyfk)0 on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 3 6 dme2qidx(:c2m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exm q26c dei:x(derted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor)ezle jt*zd68k1l-gf will its minimum braking distance be increased, assum -t8egjefdk* 16ll)zz ing all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a ,3 u ss 6hmjz2xpr5nyj5p2k;rlevel road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic xsn56s,;r2h ju2p5 3mpyzkjr 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 oia5,(g*p qnsfg6k . eif 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average e(i.g,*nks5 g aqi6fp 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 straight up by someone who does 80jget ba/bu21 ,.0 J of work on it? bt1e/u 2b, jgaNeglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a singl8p (e700eaya 1 nhjldeltgh*/e cable. Den h eh8la0 tgl(a*1d/epje y70termine
(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 const l f(upwm5 u:c.z3nsub3 a+ng8ant, k, of 440N/m How much must this spring be stretched to store 25 J of potentiannsf3 al mp(czu: b5g.+uuw38 l energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 2*t; yz)6tp0jfnvc8 hvq0i s sm higher. What is the changes )nh 6*t20i8fsp jqvztvc y;0 in potential energy?    J

  By how much does the gravitationalxk )3 +csrin9e potential energy of a 64-kg pole vaulter change if his center of mass ris ckin +93xes)res about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h w;ik vj/qe b.4qhen it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. j .qqvb;k4ie /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 gob/ elm r ignnk7:b5q 8hd*m11round so it is 2.20 m above the ground. What is the potenm kd8on qihgb*r751 1:lm ben/tial 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 f/jt +cbs+* heelevation of 1600 m and climbs to the top of a 3300-m p*h+t cfb/s+e jeak.
(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,ol zk .3ejxn*x x,oh6 of the spring is next to the 15-cm mark on the ruler. Ifoxo nz, 3eh,.k*xx 6lj a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine hwy v:3x w3isc;anging vertically from a tall tree in the jungle. How high can she sw:ci3y3 wvs xw;ing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionles:1m 1jblhxg -j+dk-nqs 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 shr gs521bf c00udqd o7kis4w9zove 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’s kinetic energy is transformed into gravitationq p21jb5* ew,uqccr+j :: zhroywzg( (al 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 2.10 m and crosu jjzewrzp y ,rw b*cc((1:q:5hq2 g+os the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jump;y(eecx1,dnci0v xyk+ py /v3*og -pss vertically upward from the top of a platform with a speed of 5.0 +pg,/x *ekyx svc(d-p iy1 yevc3;0onm/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constant)1 ajw6w.,vr(le0odm ii xjk5 is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it g,x jjwrli.1i )0 k6edo5vm(waive to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped 4qx6a4;z,jpj.y h y lftrack shown in Fig. 6–39. If the block is to remain on the f4 az4xh.jyp ,;qjy6ltrack, 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 th )um0 5bmsj 6thuj7dywl84y) xe end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacem6 jj5h)yty)s0 wl74 8dbuxmmuent $x_0$ 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 cord2wmpfwfed4 8u b,q)gb/s t-*d whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assue-g4qf)bt/*2w ms b pw8duf d,ming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster ctnts gk(bu3jlp )h) -3tig19. v f+ijpr egg11ar shown in Fig. 6–41 is dragged up to point 1 where it is rel gg+bp1thv3sgl pufrg(1i). kj nj-t)eit913eased 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 angle of,nz3c ecp5le 9 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 place;:2pa.- z5svje abjajd 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 undeb jaja -;:v2.pjzea s5rgo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyc+ /nghkgp:)lgme( .;z(thjyq le up 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 kg and traveling 95km/h in u g30lp)bus ib:dv +9sopposite directions, collide he9u 0+3)p gsuldv bb:siad-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 yh4x )g ,tx:xwa slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was ge, y t:)hg4wxxxnerated in this process?    J

  A ski starts from rest and slides down a 22 oo ls: /2lwj;e2t38 ;vdagia qe1 iit5$^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the groundvsmf mvl2g 44wr*m3b..
(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 2l,fyfiqw+o7pw g( s(m, and it bounces back to a height of 1.5 m.w2 7g(y,spqifw(+o lf
(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, isp-7u+q8)i7za+u c(cyg neq qc pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is q p+g+ z7 qne7uyac8icc)uq(-the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passe 49m phxhu0hr.s point 1 with a speed of If the apx hurm9 .40hhverage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady u) 7.h6eewzp yppward 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-grq2d :gyvv 0 is firmly 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. Whv2d:g0 gv- qyrat is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attachedgt ra- n enu).(1-j8evpacq0u2nct5v 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 compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position wilv12qc) je-(tupaa ne. tnv8u5nc-rg 0l it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 k3a1*h rx bffsf3);mh. kl .kxyg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200k ;. )k x1ys b3h3hrlf.xkmf*fam/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 pn ov95 e :.xwko+ os)h/zyjag;iano to a sixth-story window 16.0 o. zs9egxyaov:/ w5ok); +jhnm above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the adxtb80mzrb-jh-hz. 3u-se w(verage force exerted on the car due to friction and arzswhuh(-.tjdexz mb 0-b- 83ir resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.*o/okuqf y hbvt,c.g :v4nvyc;g(g *+ 4 s. What is the averag fcvggg/4qc(+v;:vb.y *t*yhukon, oe power delivered by the engine?$\approx$    hp

  (a) Show that one Britik5y4 (e f) h(x8*ml2jmyie zlmqd0n0 ish 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 “kilk x /;ki3)i z(w)e*tlb,qybrz owatt-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 6gell ok:wpw 1;0lg)ycar slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Apgpk1l:leygl;) ww 6 0oproximately 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 in 1.0;.24d2fk3lp ;hs ijgqgs nk5s h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motionn;j y0dkz1 7jj takes 1.5 s, what average power was deve0yjd1nkzj ;7j loped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m.so7hqx/2jr8l+ 9 mqn h What output rating (watts) should tq9mns8o2/ hj +hrx l7qhe pump motor have?    W

  During a workout, the footballwk*mjqb kmd5 p6 tgnoiz0l(zb6. 6(:g players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and it0m65zdz np 6ilkmgb.( k6w goq (b*:jnclined 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 cyclisu(5 p/1bkkyie5 vgn8ht climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hz -(9zowrp*q hill can it climb at a constant speed of 75km/h if the frictional forces add upqwph(zr* oz9- to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-cyjia;of;3hdj 8 / 9gekg box along a le;djjg/ ca38;ehi y9o fvel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down x8,mi/um+ bqo,:pzul vw an3: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 tgp4k3wo3k z: i,we7kohwg /+ 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 the car has a mass of 1300 kg and is tested by ramming into a sohkg ig73k3w: t k4ope/o+,wzwlid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm offha1yqj3mhqkgk ;* , n)1q pq7w the ground, and the remaining four shelves are each sp3hkk1 )hwm nqqpq y7a;,g*qj1 aced 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, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous + u/fyt:(rt b- web11vmtghu 0long jump (Fig. 6–42) in the 1936 Olympics shows that his center of masst:/v huf b gt1rm+0we(1ub-y t 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 the top of the arc?   m/s

  The block of mass m sliding without friction alofb) isjq84 l1r2s-eg (senv 0qng the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the ves 0(i)e8 -g1bel rfj4 qsv2qnsry 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 fd 5cak: d:gdn8mkmn/ 6rom an aircraft without his parachute opening. He landed in a snowbank, creating a cratd kc68g/ ::d5nmdmknaer 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord g33-/d fyqi trau13cmvd6 7owof length L whose other end is fixed (Fi7q1tr-o/ a 3uic3w6 3vdm dfgyg. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. T xwc :-eg ytytx(u7c*2he climb is made in 5ywy*utx c-tx g(c7:2e.0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator 5fss6i(;d2s/ t6a8vyoui*mn 2 f kpgcis 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 a zf/ omlp.fs.enb. 75can move 47,000 people per hou bf m.5..nelz7fs/pa or. If the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falt:)wi3 u s4p8mmjsr yzg94f4 vls vertically 81 m before striking the turbine blades. Calculatf ) jugpi843 sw :rmmt94yvs4ze
(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 di m,(3ylwy x45p xwfan4fference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depen( m4xlpxw3y5yf 4 ,anwd on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy barq 9h8f+o:.brlw/1nf )nxv gz i directly into work, how high could an 82-kg man r+lv ng)8b: n/xf.zq fh9i1owclimb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upyd(ty: 1z1 x6nsuy/exx6y q9gward 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 sc1vs2qk y2py x wbw(2z(ale compresses 0.60 mm, and it tells youwbv2xyqs (p122zkwy ( your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings ou7i tma7 qkh.z 1.vbja2j3 fs7xt over a lake (Fig. 6–45). Hi . 7j.7q71z ava2tmsb3khjf xe releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m+vdovwciaq152b, y d ) in 9.0 s. What minimum power output was used to accomplish thisacd yo 12), dbwqvv5i+ feat?    W

  Some electric-power companies use water to store energy. Water is pumpdq5v1qa:cumae3rh 3* ed by reversible turvd q mc 3hr*1:53aqeuabine 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 half. Wheawr nqbj uk q3i :t,h/n8+*uyqx;l.+at is the spring stiffness constant for each of the two res:x +kbju+n i/yq.h*que,l ;w n83 aqtrulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough ke-rv- fzt/d5 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long will 3e-u)hvaj 8hvit take to accelerate from 55km/h to 75km/h Assume thh-)hv v8u 3aeje power stays the same, and neglect frictional losses.    s

  In a common test for cardiac f1l pp/2pzq/0udj p eb5unction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estid01 jzel/p5p/p buq2pmate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 m, whatu. z ar;mh3/dl was its velocity when i3zlam hdr ;/.ut 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 amu yd(em2 ooqo,-li4eptz 2adsi //a.h8ca10 rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum powere2ou,q1cz. lm(-ti a4yde0asaoi/ 82/omhp d output?    W
(b) What is the speed of the water as it hits the wheel?    m/s