In what ways is the word “work” as used in everyday language the same agtk, -cc*/rh dh ycpv0 z737pbs that defined in physics? In what ways is it dy ,77c*3rcp zh-p 0cthk vg/bdifferent? Give examples of both.

Can a centripetal force ever do work on an object? Explj5e frjhuk-4l1s-2 gh ain.

Can the normal force on an obj o o-v*cyc16mr39dx vc3ni*tu ect ever do work? Explain.

A woman swimming upstream is not movingvspx jf4uvwem)b2cx 6)4qf e).x ar8 .:lna :y with respect to the shore. Is she doing any wo) p:ayvab.8xx).e) jvmc4w46xsn :2eqf r ufl rk? If she stops swimming and merely floats, is work done on her?

Is the work done by shd+;eyry4-k )pbas, . se r1ukinetic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from undyus. +rpdbh,a sry eske )-;41er them.]

Why is it tiring to push hard against a solid wall even though you are do f o4k x bzpnfor/7l-8k/o/ug8ing no 7o k/8kof/lbzru/x4f o-n8gp work?

You have two springs n3uddi2ay1 , vbohr,, that are identical except that spring l is stiffer than sprinnda,d1, y oh2uv3rb,ig 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 slide on aaqjo+ - x:gwfs /)dcyd5az5)n frictionless surface (Fig.6-30). Tfa- /cqdz sy+j x5gnoaw5):d )he block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational q+v71(qnfr(7kft j(h y(it fy potential energy change when you jum(tj(t viyr(fy(17 7q+fkhqnfp as high as you can?

In Fig. 6–31, water balloons are wq9es6 t4x0)+t oagfl7q1 fjctossed from the roof of a building, all with the same speed but with different launch angles. Which one has the hi+cw6g0t qfaqoslt)x j9 f 17e4ghest speed on impact? Ignore air resistance.

A pendulum is launched from a point thom- 8xh+.gdfe at is a height h above its lowest point in two different ways (Fig. 6–32dogx8 .h +-efm). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. 1jq5o c7ibh)(r yuq/fenx8)y If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using 1 noqy5e))r(x7 bcu8fiy hqj/the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33 u7 b(,+ rjhnnr j-xpp/k1dq7t). The instructor pulls the ball back and stands against the wall with the ball ag,d/rkn +uxq77tpj h-p(b n1jrainst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when watea 5v ifspxwz y5p/m2u( 3q6c*dr1*vker at the top of a waterfall falls to th55xuvz(spfr ya 6w3c 2/ ikep*md*v q1e pool below?

Describe the energy transformations when a child hops aroundoatqpb2h7 n:, on a pogo stick.

Describe the energy transformations that take place when a skier starts skiingvxm8sfo*,d e 8 down a hill, but after a time is brought to rest by strikodfm x8s8* v,eing a snowdrift.

A child on a sled (total mass m) starts from rest at t/eoa4 -kfhc n4he top of a hill of height h and slides down. Does the velocity ch4en-foa 4/ kat the bottom depend 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 theie+j+1 mias (evr path rather than stepping on top and jumping dee +v( s1j+maiown on the other side. Explain.

Two identical arrows, one with twice the speed of f5nhoenw j- 5j nxwcnb :(5r:5the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower a:5r5xcf- n 5we:nnh jjb (nwo5rrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (k af6d bklt)e/ 5xj+3ya) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has t)5 dxl6+bae kfj/kt3yo be wound up.

When a “superball” is dropped, can it rebound to a heig + 7n*mbsh);gidza5gn4n *s aoht greater than its original hehi za 7) s amd+n4obn*s;g5g*night? Explain.

Suppose you lift a suitcase from the floor to a table. The w.0fkpb exk3 / bzc,ey1m+2q6y; vqt wmork you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a moreyefc3k pb16,2m.m0+ ;wbk /yqtzq x ve 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 0- wxh2/uxfs-jy u1me needed rather than the work.

Why is it easier to climb a mountain via a zigzag t1yil7 w/-qrt4t c 5j1miq2euq rail than to climb straight upt11mt l4 i w-j/cu2ryqqeiq75?

Recall from Chapter 4, Exampl*br mb86(pndq e 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 forb m(qbn d*6r8p 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 when a 265-kg pile drivennj+ 48f:f rtxr falls xnj4+n8rf t:f 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stz6cnz,vr/ j 8iairs 20.0 m high. How much work is required? cj/zi68z, nrv    J

  A 1300-N crate rests on the floor. How much work is required to move it f4zb : o1y8kiaat constant speed (a) 4.0 m along the floobk4 zi1: ya8for against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (hor/)+ )roika; eo,2loyp xdgd qh* +c:xrizontally) pushing a 160-kg crate 10.3 m across a rough f pocrxh*dqaxe;,i 2yl: / +ordg))o+kloor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a f,pb;y5k 1igw2vwa* oo/n b 2rzorce across a floor at a rate of for 7.0 s. Find the net work done onzon1b*k5pwi a br;/2w o vyg,2 the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, dq )xma nqe,k;wu a;2*lie flat on a table. How much work is required to stack them one on top of anow,*da;ae; kn x2)uqmqther?    J

A lever such as that shownzjob92)+rac b in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Shc9orzb)a 2+jb ow 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 o v6f)ze g7b/m4nz; qqand 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 fob 7mqzz/g 64;)evqn0.40. 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 r 9,kk6mf ,fnzzequired to give a helicopter of mass M an acceleration of 0.10 g u,f kzzmfn6, 9kpward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linea big 4;0rks4nvr and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in F3hkt1l -s.g yj-ol0fi (omzq 5ig. 6–37. Determine the work done by this forcyz-51s( qj3k.t gilohmfo0 -le 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 onl rb rn9v )6(;jb+uuto a particle 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, an3q ahsiui70 h 5j1,hmm oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doz7k t,m ,5rqklubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is require,y bi-yukxpk04w);c :hurk d*d to stop 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 bc)q9dk s glbs+nul216 yr3(hvvw2s3d e done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of 110w uklh3q0x b2wdtw+o/ o l4b4/ N on the arrow over a distance of 78 cm. What is the speed of the arrow as it letko x2 q0+l43lho/b/uw wb4wdaves the bow?    m/s

  A baseball (m=140kg) travelingm)p9 aerulfc760ou b+akg.2 e 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by t0lkfu7 bape.)e6um9c2+gao r he ball on the glove?    N

If the speed of a car i,xubdb;xsy8vmo( *t 0s increased by 50%, by what factor will its minimum braking dista,x *m(ous x0b;vbtd 8ynce be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark0im; )o*g5q qy:xd, z f /+iwvliaf/gb to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speedaif0 ixmg*/ql iw,y5)+ zfq; g:db o/v 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 kgz)mh6jy:bke e 8y4n1j is pitched at By the time it reaches 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 pitcher is abo:nj1yzhj )kb4yee m86ut 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80.0 J2* l5 ft*rpkqf of work on it? Neglect air resista2 f*lrpqt5fk *nce.    m

  A 285-kg load is lifted 22.0 m vertically with an acceln3ygaj 2 ln+f,eration by a single cablefnj3g2,aynl+ . Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much must thexmv k;*vueo4(z hnm,9:ro /his spring be stretched to store kvhem r94 *ex / ,o:;(mhovunz25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Whaesbqguq ; 3v9z n/ya.7t is the change in potential v/;bq gsqyez.3aun9 7energy?    J

  By how much does the gravitational potential en(2f80 j2no k dzj6lxzmergy of a 64-kg pole vaulter change if his center of mass rises about 2mjz f(lj62n dkz80xo4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h w.ss(1;(/r *dysmuwknte/ w sw4zzkn3hen it strikes a horizuw1smyzwres/ 3z*n(k./ w k(dst ; n4sontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so io3).p pg2, i3ft9zdhofo u rc3t is 2.20 m above the ground. What is the potential ener2.gc9 ,i3tdu 3hzf p)oo pro3fgy 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 h5dg6hh;ax2ryv ,nu 7 an elevation of 1600 m and climbs to the top of a 3300-m peaky ua, rv7;dnghxh26h5 .
(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 t/7wsd.royv avr07 90x58j:pu pnu soz o a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now dup8/ v wa:95r.unyz 0vx7osrj o7sp0attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzag *pl a.-d7vvsmhm+6w n, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she-7p+v g* vm.was6mlh d swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rnne, weoopckim h87y3y, 6cd1(- yy*aest, 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 lt* *cxlj h4*lc+v; wga 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 gravitational pote)tnp; wgf gk+9ntial energy without the aid of a pole. With what minimum speedwk )9 +png;tfg must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vh z23xctof1nrk j,t5bu 02nl+ertically upward from the top of a platform with a speed of 5.0 mxc21n, h3k o 20lzt5+ ujtrnfb/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 stiffnte.q ctj7c.4lct +tf9 ess constant is 950N/m is attached to a table and is compressed down 0.15tq +efj7t49ct ..ltcc 0 m. (a) What upward speed can it give 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 loosexw6r7o2 . s t+2jrlaped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it bew2 srxea 6j.+rs72 lot released?    r

A block of mass m is attached to the end of a sjqajh v )z4,c6pring (spring stiffness constant k), Fig. 6–40. The blockvh, )4acq 6jzj is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose sr9k) ;di nrkf(:0eh ounstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffnesfhr ;(ione0)d:krsk 9s 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(2 pt4tco*hvp*sx 4kbny/,wn * e,cro dragged up to point 1 where it is released from restpbwy *nsc, k4h*tx/eor v 2oc,4ptn(*. 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 a lpwa ,w ;*jgxi 34ljcq:(7ly 3xqcz 0f5wi8qm/s at an 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 plgvh f (qzj(3x mv: 1pqfova4 t8:o d,nmrv.p,0aced 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, calculatemp v1nvd (ph:g,a. xf,0 (j8vmotfqr3 vzq4o: the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cypl(l.zmcv: 0 jcle 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 opposite di, /s70 nt+l+z*sde6. ftirde-vzvx iirections, collide head-on and come to rest. How much thermal energy ii7, v0 .ttlz ds-+xrnde6isvi/ze +*fs produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom wit .m/(w e9qsozlxd.a9r 7,nmoyh a speed of 2.2m/s Ho7/yln ,.md9 zamwrxe(o q 9s.ow much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides dzn y9(1ajhf y)r, tpjm1nos (2own a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13 opcref6z+( v).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 heigzc*-o8 43k-4pj ifusi deub5qht of 2.0 m, and it bounces back to a height of 1.5 mue5*p4 i ois- c438kbfqd-uzj.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a fl- lr0dfrn+/g*adu 2dz9l pwv6oor 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- wrud2fd 0gp r96+z*vna l/ld. What is the final speed of the crate?    m/s

  Suppose the roller coast6) m vr8)1zglez h(as ju2by2gkgl s60er in Fig. 6–41 passes point 1 with a speed of If the average force of frictionm u)zseg60(vrbgz1 h l)g2j 86a sylk2 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( 28p o qif.82am5bkqjp s6wtjgag u34 the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block i2,a)xv2x vphms 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 rp)havxxm 2, 2veleased, 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 horizontahus *7;6ua a,,.hel c p7jzzcjl spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30.zjl6z;e., c* 7u jh7hp,saacu A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg inclu0 (x0k yvik ohm)2a5rwding 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 would its landing speed have been in the absence of air re0w0)xkry h( ovm5 ki2asistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sifg-p9v. h45 dovup/vi8l16 p9ncgdo pxth-story window 16.0 m/4pv6po gh9pcdfiu5gdovp 1l 89 .vn- above?    s

  If a car generates 18 hp wa rin+/es8iiax3o k4)hen traveling at a steady 88km/h what must be the average force exerted on the car dua 3/4k aosinix8)ri+e e to friction and air resistance?    N

  A 1400-kg sports car accelerat x f0+.5qj7:d ikneadho ,uo2d;jx p9pes from rest to 95km/h in 7.4 s. What is the average pi0a.;jnqde 5o h9:d xj7f udo,k2 xp+power delivered by the engine?$\approx$    hp

  (a) Show that one British horshmabt-zt. :7z epower$ \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 dz3w0dw zuosvgj 1 ja8 ( t9(3-:jjxnmthe 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 a91nf:l4; ibuystz.h3m -j p zkbout 6.0 s on the level when it is in neutral. m3th1z: kp;zfnjbusyl . 9i4- 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 in 1.0 hqu 1xl)bf m6n*? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from r6qejscd m 5*s9est to 14m/s If this motion takes *c5eqms 9 j6sd1.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a .*s ra-j6gvrncu:fx; c x tw57height of 3.60 m. What output rating (waxrrg . xsw56fa:n -*cv;ju7cttts) should the pump motor have?    W

  During a workout, the footy32,vt*ul: ckuv u 2ca)uouv :ball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 2t )uk :ucocvu*,l3uau:v vy2m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0xrut96rgqef12e uj+j j3g-wb8s -q4bqqs6 z; $^{\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 12/k3o c0bxft2v qxg4 (c0 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forc(otcq/x2fg3bx c 40kves add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to 2uj u)g1e*b11 vomjr dbe able to drag a 310-kg box along a level floor at a spo1)ed1j u g1jbmv*ru2 eed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a xa7jd**k ey6a *,icpw8k :ic c7.0 $^{\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) bh/z- fxf*h ,iscir (;wcgxv7f7y,1 jyumpers” 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 fg cy, ;hs1wvxf -i(zifj/7 xh,7cyr* to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the firscr54fq 0 btdr3t shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill atc5d f4rrb30q ll the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympics. xgm/h1f7- mgk gjhb.g/ l7b27rx zcc shows that his center of mabghlz /.k x1fghmc2/r7 b-mjxc77 g .gss 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 withouvqthn0., xvns;iic q ,.kiv)n7*e r1 rt friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop oics x tv.)rv01n,v, .ih;nq7n eqki*rf 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 fe6 sk,.n,2n 2zg3m4llzr/fcmyrwp v2ull 370 m after 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 verk2 un czm2,w/ gsr .lf vp32m6z,ynl4locity 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 tofn c+v.6e hmp/ a horizontal cord of length L whose other end is fixed (Fig hv.emnfp/c+ 6. 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-hj6zf ef7iu6t0 igh mountain. The climb is made in 5.0 h starting at an elevation of fze fjut76i 602300 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 is m/ .m -6-kfnnati.jjo 1wlj1 r28 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 cpgij (xz4,g;o yl )o1blaims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) hiogg;y)op 14lj zb(,xigher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at t8y;q bgf/ bug1fg,kewe24an2 he rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculat2fygnf eu 8q;b/142 g ,gkwbaee
(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 coas, bbl5 /bqfx*tukpyo*45y1p m ter with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — 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 dmuf,*x4 ybb plbkyq*/5o5p t1 epend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, howdboze.w*+vv 5 high could an 82-kg vdoe w *zbv5+.man climb 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 firedo*op636v +y3mklhfom at 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 compresses 0.6z7sj,tko uug(*df4fttx +/e60 mm, and it tells you 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 it xttfsf,ogz etj67u(/+4 *kd us peak?    N

  A 65-kg student runs at 5m/s grabs a rope,c;/5q/bk tmux id j0q 6kve0+i2e3hmw and swings out over a lake (Fig. 6–45). He releas0dmwmkqe exbu q2i/i/j05;t c +k36h ves 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 disqc6wj0u*a7olco;c v - tance of 5.0 m in 9.0 s. What minimum power output was used to accompl*o;ucwc j vca607l-qoish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by revex1vep*k r1s3 ike)ws-x2mc :trsible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hs* x3t21)kxi1r- smpcew: kveour 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 consq jpwiv,b +u;)tant k is cut in half. What is the spring stiffness constant for each of the two resulting sprbuivj p;q ),w+ings?   k

  A 6.0-kg block is pushed 8.0 m up a rougeuto*(yey3-rh0al m /h 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() h)whw x)tx.b2uj-v1qcbzp in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the s)xcvpxuhb -zh t) )jw 2(.wb1qame, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the pa 9tz5 h +xwzx5plg,,xstient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sg5 9pxzx,5wl,tz x +hsloping 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 b4k qdv2ul)q: o0yv.bof 500 m, what was its velocity when it left the vv dybk:2uvq 40bq l.)oolcano? $\approx$    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 wa amtx7q(lo vs/1 ch/3nter wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricic 7(3lshm/a 1qn /votxty output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s