In what ways is the word “work”;a3-* (b boemn,6 ,dbsnwm gdh as used in everyday language the same as that defined in physics,bn-dhoe6(bnb; smg*3,dw m a? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an fn(/3c2r q1yluoq -zi+wnb r2object? Explain.

Can the normal force on an object ev d,/fuaj dt-havfou h5 .9;,g .pf,weder do work? Explain.

A woman swimming upstream is noi8x( 9o, xwjsdzap dw4 );e+yh pt-sb9t moving with respect to the shore. Is she doing any work? (is;)wx+ e hbdd-y98apw toxp, z4 sj9If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction f 1/lrm+an-xn dly7q-c -4q avuorces always negative? [Hint: Consider what happenny - qalcrl/ma+d7x q-4uv1- ns to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even e snb:k5-;.k .hmww cdthough you are doing no wom:s.ek;.ww5nb -c dhk rk?

You have two springs that(8zo ya3k ez5y are identical except that spring l is stiffer than spring ak5 38ozez(yy2 $(k_1>k_2).$ 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 hoyt6i7w3b dx8j rizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has xiw687jt d yb3traveled 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,4 w xft1ghym7ential energy change when you jump as high as you 7fy,4t1hgxmw can?

In Fig. 6–31, water balloons are tossed frp;(fd . sh/ vm,nu/k .mgo.3iryht6lq om the roof of a building, all with the same speed but with different launch angles. Which omomlpf sqnk /irv ,t;.ud3/ g(hh.6 .yne has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its )y:e +:bns(syc7 shd5udta 4r+vn5dn lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest :n ed)ysnd v+ sby+u75(an5t c:4hdsr angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compressh4pv q;:x 1li*6 afldraex; a7 the spring by pressing down with your handq; *er lhx p;7ldvx46:fia1a a and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung f qvpwig i);c-3rom the 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 withw3 icv-;p) iqgout pushing it. Why?

What happens to the gravitationab5znd -3 (vut;r5b3 h.xcolgn l potential energy when water at the top of a waterfall falls to the pool below?zguod.htnl3r3 bv5x- c( ;b5 n

Describe the energy transformations when a child holrp+vjje ju(e,zo1 9 kynu *xx,yply/*jc-(8ps around on a pogo stick.

Describe the energy transformations that tat(q; ix a-ymvd c.u-n0ke place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdr; d.-ucimxq-(tn y0vaift.

A child on a sled (total mass m) starts from rest at the toag8(.h8cul. v j6 rrmbp of a hill of heightc.bg6(.u vlr a8r8 hmj h and slides down. Does the velocity at 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 fazfpw0al8 i1 1vg (ikqhzsl.n f/1,6kz llen log in their path rather than stepping(v8iw,zkzgil 1l kq61 /fnfshp 1az. 0 on top and jumping down on the other side. Explain.

Two identical arrows, 5 ajn)hwb7xop)wqf;f2- j kw)one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant fric7wj n fw)wfab-2;)h jxpqo5 )ktional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a js(xw1l8k1 nj u-qy o5simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction i8ox-1nk y1 5ujjqw s(lnto account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it reboundsv8 f2ic:vr-zd r;yr5l lin a7;ksv-: to a height greater than its original height? Eszr7 i-cdv5 vfkyvl -:2rli s;r n;a:8xplain.

Suppose you lift a suitcase from the floor to a** 4n5mfq9a u3vgt xkf table. The work you do on the suitcakn 5quv4 **g9fatx3fmse depends on which 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 rather than the wg(;eyjjisja7mx*l6gj / v xtq 4m;- 7work.

Why is it easier to cm6y ,ski 3ibv,limb a mountain via a zigzag trail than to climb straight up? m,i ski6y3b,v

Recall from Chapter 4, Example 4–14, that you can use a pulley and b 7mooo6xucyqw )*u4( ropes to decrease thec)* mubyw6 (oox47oqu force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational jvdvl;db3 -izma7+wycr62m hb)-28 lz7ivmvforce when a 265-kg pile driver falls 2.80 + b2hl7idwm6mzdv-8byc;z)-2ivv 7m rajl3 v m?    J

  A 65.0-kg firefighter mnhk9 w bnti3 baz6fpi*2 8+b.climbs a flight of stairs 20.0 m high. How much work is required?9mbn+a3 i * k 8itpw62fhbzn.b    J

  A 1300-N crate rests on the floor. How much work is required to mo0id: +7j yvhawve it at constant speed (a) 4.0 m along the floor again:h7jy dw0vi+ ast a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the move6n 0)nf vieb2hrs do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effe2 vbe6fin n0)hctive coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a ru -x.a/z 8qh *ktpz+t dqsft77ate of for 7.0 stq-8tsha tz zu xpd7/f q*7k+.. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mal(x e+1t : eipnb9-.ogiwb-qess 1.7 kg, lie flat on a table. How much work is required to stack them one on top 1e nie:qewplb +g ib-x(-9t.oof another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects wefp7,mbhx ks0gf6w * mv697rxq might not otherwise be able to liff.gpf hqx* 6 7smwkb07mfv 69xr, 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 mu--p qom; ;enh down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficientoqn ;; me--phu of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give0y,id6 6oy q 3(flpfmlixx z(1 a helicopter of mass M an acceleration of 0.10 g m,f(1poz q 6ily(6xxfiyl0 3d 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 is line*xvzd - z5kl+mar 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 shown3e(d7 j czqn)f in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x =nzjq73 cd (f)e 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 particlu1v wylnuh /7:e 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, anfg bb;rq;z 3t *rx9o,e 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 doubled, by what factor has its sp/-r n c:,70n scx)oj yctu7ku,cdw-upeed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to c3ud g*lh q3+z b i ;2iosa0r9 x,6p0druz:thtstop 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 sth6- l;omjtj x r7vu*j.op a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bon* )x4 clhl;1xltl; tww whose string exerts an average force of 110 N on the arrow over a distance 4*txl 1w)x cl;lhlt; nof 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 35r6d3fyowp;g)z uc zcm when the ball is caught. What was the average force exerted by the ball on the glyfu)o r w3p5z3z;gcd6ove?    N

If the speed of a car is increased by 50%, by what factow .3gksd0t rd87e myh*r will its minimum braking distance be increased, assuming all else is the same? Ignore the y3ewm8d0s .*kdg7 thr driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark tn 3jl8n n7y(a,1kyg ifo be 88 m long. The accident occurred on a rainy day, and the cokg7(iyynf l8a n,3nj1efficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at B e+isc3mxy 2.ky the time it reaches the plate, it may have smkec.3 2xs+ yilowed 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 straight up :da1.b: yxsh fo/3r wmby someone who does 80.0 J of work a3h / mbfwry:x.s:1doon it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an.3o 8ulx gy(id acceleration by a single cable. Determine oiu83xdy . gl(
(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 Hoq lu7f vsdc8pvo2q lmg9;j 62/w much must this spring be pd97 2qlmc s8flo2j vvu6/g;q stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings fr9o;e*2fr5wuscccs k . om one branch to another 1.2 m higher. What is the change in potential scs ou5r9*f;. 2kcec wenergy?    J

  By how much does the gravitational potential energy of a 60ny e6 :lhhrm04-kg pole vaulter change if hisem0hlny :60hr center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h wher ec dznn*-sk z*y*)rk9:p+ ian it strikes a horizontal coiled springskei+zay:kr 9-rz** nc) *pd n 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 grouhvza f3x02,2iw d0 rdhnd so it is 2.20 m above the ground. What is the potential energy of the book relative to wavdi2,d2f0r0 zhhx 3
(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 elevati: x0s 5mxemy9fon of 1600 m and climbs to the top of a 3300-m p sm90 mf:xx5eyeak.
(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 spr qs)j1(li 1w5 wa-cmtnfq)j /qing i1fq5q) 1/l)-( ciwjq ajs wmnts 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 marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine 0 cr6xraebvi z 5bdd2.af55l8hanging vertical6a5d5. 8dz2bc 5lxfe ria0brv ly from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from ra3. v l pxvghk2j8vu7(.ev9)yk u4jpl est, 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 1rxtqu s8z f2zd;jd9nk6 z7c8 shove 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 kinewgig 7o3( u) 8fltuzg(tic energy is transformed into gravitational potential energy withouto8) 7(3gtui zglw(ugf 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 cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upwawwnt2: .q ur9e6 4kuev2 ok3wvrd from the top of a platform with a speed oq4kr. 2nw3ww u6kv9ve tu:2 oef 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness cnew:fa7e8 :2khkd l1aonstant is 950N/m is attached to a table and is comprekdek8w nel12 : 7aha:fssed down 0.150 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 al+ m (7.dmaow) hasasbo.8kkeg7i9+nn ong the looped 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),a (id)+ka9+h bmn87 msoaew .sn7o kg. from what minimum height h must it be released?    r

A block of mass m is attached to hh35 r: kz js0r(aree(the end of a spring (spring stiffness constant k), Fig. 6–40. s50r(ajkh r:3 e(zehrThe block 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 jbs4rwfl1pdre 7/i j; 3umps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 /4j7r1f 3pbws;lde rim. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragger 4*ei:fo6qbjldg2/r d up to point 1 where it is released from rest. Assuming no friction, calculate the speed aqrglr 6 /j4ofe bd2*:it points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with arv zs/iqkkf9+7 *1 2ew f(htu6rsojt* speed of 12 m/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 9jh/pd 8wypwr5hyu:m(2 rk5 3mlf4bjbe 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, calcwph hydp:k( l39mw5 ujrb y/5 mj82rf4ulate 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 cycle .p pmq4x592ov ccbqnp +-p7 iiup 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 ofq6w 5e-pae/ xumj v b::q*c-va mass 7650 kg and traveling 95km/h in opposite directions, collide head-/ubc6q*j w xpqeaev:v: -a5- mon and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a zr29 hirf+ z9wslide 3.5 m high and reaches the bottom with a speed of 2.29i9z+w zf 2rhrm/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides.i,b4 i,u hgxw 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 ptv)m/(:jgq udropped from a tree 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 of 2.0 m, and it bounces back *+yw t(utrkj6 asni 1ok;aif23xeb1,gu e g(6to a height of 1.5 m.t,sx;(1utaen+3we r 166(ujgi a* bk f2koigy
(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 floor with ae)d9v-qd y8ke z8(uml klvf.8 constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of f-v.z)v9 8(lm duq ldy8kkef8eriction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coast yq-u2;vet*c mer in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its wem2ute*q ;c-v yight, 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 upward 18.qnms+ ,qmfc 2jya.q 7z( q23qk0 $^{\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 blockp*.a14roi 7 +dn hijomi kdu87 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 positi* rd8o7 niiki+hpo1u . 7m4adjon before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fisi5pfemzu 43/ g. 6–40. The block can slide along a table whemisu4 f/p3e5zre the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” ,a8fmlv)4zjtbxsn66ceqpl- ( :qa 2 g(mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of airen6tpfq)v-al a2j ,s (: zmcl6bx84gq resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano tlhoj2w w;n*18c3; kfns v1tago a sixth-story window 16.03g hf1 w2os*klvtjwn;1a 8cn; m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what m/g,fyheee)y2 i 6d,jdkp*.xbust be the averagey *eehe.kjdp,ix),f y62d/b g force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h indxb/u6y h )y ov.*rh)p 7.4 s. What is the average power delivered by the *p.y dy)b)vurx/6hho engine?$\approx$    hp

  (a) Show that one British 1jv vpy8t6h:k 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 /wu :1kcv1wk(naxjqbda.l:- “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 do2wu8pe,ggi g uwl1b*1wn from to 65km/h in about 6.0 s on the level wheng ig1u,g8w1 uw* bepl2 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 in 1.04f-2/gv5ska,ci.ja ub gk p*9udv j1i h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motion takef gu* 9xnw(9n oxn*))ngbbn(h s 1.5 s, what averngf gwh9)xn9(n)b unx* bn*o(age power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minut +,hutb2bvdn-e through a height of 3.60 m. What output rating (watts) should thu-hn bd bt2+v,e pump motor have?    W

  During a workout, the football players at State U. ran upc) 40 m jo sjig(pnbp )sivzx9btf35** the stadium stairs in 66 s. The stairs are 1c i* 5in3po* j ms9p(4f)bjzvgts 0bx)40 m 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 climicp3v7b;o ru*e/q h7 db 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*v w0*r 3ljvm0lx p; /carida0 steep a hill can it climb at a constant speedxl/ca;vj0l0*0d vwpr 3mr a*i of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be mad-nkuhvm : r8wg5wq 2b3,w9able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction isq w3num akb-8,gm5r dwh92:vw 0.45?    hp

  A bicyclist coasts dow ;t* once6ylk/n a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5 - 6lyrxorf4l7*a c rbm(fer5.mi/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 isrobmfl4rrac*(5- yf. 76er lx tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the firsv dkkb( e7* se07bxs7gt 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 averadb ge7s7bk(0 xs7k* vege 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 long jump kcnz ho h8+;(x(Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the (c;x+h zhnk o8arc?   m/s

  The block of mass m sliding without friction along the loopeah(k/gjtb4q 8 d track shown in Fig. 6–39 is to rejbaq8h g(/kt 4main 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 sy81:nn4gqlh from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived wi4q1lny8 hs: gnth 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 of length L whose other end is fivk3,/icvbp;tpn3/ wjxed (Fig.pivpkv3/j/ wc3 b, ;nt 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. The-isqhyl7c du +i*.o* ,fbaw k. climb is made in 5.0 h starting at an-w.*dq kcb o 7as ,ufih+i.y*l 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 elevattozb/0hhof ,u 9;ai3 hor 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 itso90bjf l zi+5b2uxe n5 lifts can move 47,000 people per hour. If the average lift carries u0ibbxz2lf o 9e 5n+j5people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a d++y4dsk+k+0 bidbazkam at the rate of 650kg/s and falls vertically 81 m before stri+yaksk0d4dk+ + iz+bbking the turbine blades. 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 rollefkw x) y 0mj)zo17yp wv:eh,/xi+dz9hr coaster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and tjim dv)0w 9:oz,hhxxfz/ep1+wy7) k y he 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 c-lf m:y-rml0i ould convert a candy bar directly into work, how high could an 82-k - ymrmilf0-:lg 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 fired at an unrpw x3ci8rv ;/avxv(f-,2m xb 3zw *dpward 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 tzo.ykp 4*d j d 4annkf q:;i)u8otsc/.he scale compresses 0.60 mm, and it tells you your weigtddk8coojpyus:4.z /. k4*)fan inq;ht is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out gkbsmgir f5/ /0-b* gjover a lake (Fig. 6–45). He releases the rope when his velocity/0 gmi/-sfg j b*rbgk5 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 *8y*ksagtb muzqe6 7v;,zl3g vertical distance of 5.0 m in 9.0 s.z, g6ea3*lzb*yk s8;tmv 7 ugq What minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy.xlq e da:7ya3imx2q3ko .*hj1 Water is pumped by reversible turbine pumps from a low to a high reservoir. To store th *lixjy7 aq:3e3aqd2. kom x1he 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 +vikhua5)x b)spring stiffness cbu kvx)a+h )i5onstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a r*+ 6rijsg r w/;ll0jqkough 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 acceleratlb,-do-zg q egjn(2 *fe from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h2(*--gendj , bgqlf oz Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), :mwj6p6qcs-a7e+o pjt:fw )j the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill p:66w om: -a+pfw tjjs)j7eqc 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 mxvd/-u) hg(+o,qevhh , what was its velocity when it left thxd,ghe-v(vhq ) /o+uhe 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 2vr8x :8z k/x:hal-,y3)frbf5 gwke bv.0 m at a rate of 95kg/s (a) If this water g, zx :f8 blr5/ -byr38 av)fkve:xkwhwheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s