In what ways is the word “work” as used in everyday language the same as thatc:l fkui bin9k).kikub40 9 h3 defined in physics? In what ways is it different? Give examples of i)u nkkucb k.l:39 4 9hifbki0both.

Can a centripetal force ever do woryrn 3y) x)ho,he tf*7mk on an object? Explain.

Can the normal force on an object ever do work? Explaind- 7,4qzp v(qflpc( ) 5zfnfum.

A woman swimming upstk: ,e+uenz0; v k0vd+o,puy-i; wk rbbream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work dopnk-evuby0euk++ ,0ov d ;; wrz:bik,ne on her?

Is the work done by kinetic friction forces always negative? [ z hkqni1y;qdq7h3: 3 f*u(3xra5m fqtHint: Consider what happens to the dishes when you pull a tableciadfrth*51n:qq3 ;7 zx(3fyqh3k m uqloth out from under them.]

Why is it tiring to push hard agains;go l7d /bj icklw3v;sh64xs ;t a solid wall even though you are doing no wssg kdc6 wx/lh;o47lb 3j;;vi ork?

You have two springs that are identical except that spru4b)jpt ytb b4t2l 0.hing l is stiffer than springuhbpbtj2.)4 4tb0 lty 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/dnz,oq3ex4rtg63d g in )6q o is free to slide on a frictionless surface (Fig.6-30). The block starts /)q otn6r6zdqond4 i g3e3gx,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 gravitatio4ekh t c ksew,;9*rgaj6xlb/ ;nal potential energy change when you jump as /;69e;,awgk ehc4j txr ks* blhigh as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buil.wzdov8;c 271zdnas gu0 q2to ding, all with the same speed but with different launch angles. t;0csdou 21ao27vg nz.dz8w qWhich one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point thatk8 n, 07 jvss 8ymot).vorbd;q is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will caus7s k0oov8 v)rjbq .8y;tnd m,se it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you com7 c: gdc/jd3edpress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the lawgddd 7j3 e/:cc of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instx/l:tuohh/ i8 ructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to ru h/ hilo/t:8xelease the ball without pushing it. Why?

What happens to the grap((ebjzyxtp 8 0qy.; dvitational potential energy when water at the top of a waterfall falls to0. pybtz8(eqpd xjy ;( the pool below?

Describe the energy transformations when a ch4c+ iqprn p9pgl* b5/oild hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skiing dy p/d +bd ptu bm):2t5r*nltxo 7*8oqhown a hill, but after a time is brought to rest by strtto* 2d*q pu: r7 8+ )5dohntbpmxy/bliking a snowdrift.

A child on a sled (total mass m) starts from rest at /tol9a8kb+n othe top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of/l+ o9 8ntakob 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 fah oscyc16+3c allen log in their path rather than stepping on top and jumping d3 ycs1acohc6+ own on the other side. Explain.

Two identical arrows, one with twice the speed of the other,yvd- p1h vzrt;wr; 8n9 are fired into a bale of hay. Assuming the hay exerts a constant friction ;yrd1; -vrwvzth8n9pal force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in te k ;4t1d8ovus phiiu64rms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfato 1vi4du6 phuki4 s8;ther clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greatehj /rl50 ki/ob)xf7:k fvli -x0hhlw 5r than its original heilohh / 7kjwk500/ )lrlxx b-fh:fiiv5ght? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the sugqrvouf:;y: ;xb ( b+q(8amlf -lyh7jitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the tl;m: ql7 ay:(y+rf (ou ;8jbhfx q-vbgime 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 work.x8okar 2u1e-d qs7;n r

Why is it easier to climb a mountain via a zigzag trail than toro)v j5z k7a3k climb straight uz v)kak 5o7r3jp?

Recall from Chapter 4, Example 4–14, that you can h, 3cqft86p kvd7g3gyf/ rmh :use a pulley and ropes to decrease the 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 cgt37vrp3qk chf6/8d h fyg,m :oncepts.

  How much work is done by the gravitational force when a 265-kg wt v*7yselw+.;2s jfgja 47 bvpile driver falls 2. jj2yg vwt4la.*7+sf7w vbse; 80 m?    J

  A 65.0-kg firefighter climbs a flightxv6q:i (.vc r/drso3tt viz.we;j /e*dl* /ds of stairs 20.0 m high. How much work is required?sd6itrld e./vwzov.ve*sdrt c/* qx( / 3;:ji    J

  A 1300-N crate rests on the floor. b3 wrl9 ;welh)How much work is required to move it at constant speed (a) 4.0 m along the fl)el w;hwr9lb3 oor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do jud5bz62m1z s (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effectivjbmz12dus56z e coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a flwsg+s1peu5 g-oor at a rate of for 7.0 s. Find the s+1gseu5 g -wpnet work done on the box.   J

  Eight books, each 4.3 cm thicv3nieeln4y.u i. ,wq*:d(pxk k with mass 1.7 kg, lie flat on a table. How much work ixi(leid,nyq. k wn* e3uv:. 4ps required to stack them one on top of another?    J

A lever such as that shown in Fig. 6dxl nj2 rfawd*) cpfr u0u3,:(-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output: p(luan2rdffx ,) ud0jw*rc 3 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 fm02 cm61fakp nxr63u m 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).f prm6xmu3 2nk1a6 0fc The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give nm6)3k0c gp jpa helicopter of mass M an acceleration of 0.k)p06jmp cn3g10 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 l6kib :vw rq1:axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the vf 9 zdyxh219xx axis, varies as shown in Fig. 6–37. Determine the work done by this force to movedf 9vx1 zy2hx9 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-hfiw 2 i+n5xw 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, v;k0rxq ,y, oub+hn*lan 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, byl z2k9wvf 0w*b 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 required to stop an elev,qn 5md zgmx8+b;j +tctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-kg f4)db.rqt lmptr+8a nnlt 3/:car traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose/b7crf8 wvckd;jma0; string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of thew 8c jfvk/bdar0;7;mc arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves x/e3 -u; dnare3aqr c0a fielder’s glove backward 25 cm when the ball is caught. What was the average force exean;qr -xreed / cu3a03rted by the ball on the glove?    N

If the speed of a car is increased by 50%, by w-f+t)prb *ub4c 0vakzf 0an .xhat factor will its minimum braking distance be increas)f un-b cbazt4.+px00 *fkarved, 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 sk 59m0q)zhueoz id mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. 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?) uqhze50omz9 )   m/s

  A softball having a mass of 0.25 kg is pitched at By the tid t gchl59,j:jme it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if tcgd jlthj 9:5,he distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straigh8 u rojq1320inkomdw-t up by someone who does 80.0 J of workio8q12dk-ujo wnm30 r on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an a2jpts(whp 47vo f1sd 4cceleration by a single cable. Dh 27fj wdpsop1(ts4 4vetermine
(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,/vn.bw +gb,etk 8)i vr k, of 440N/m How much must this spring be stretched to store 25 J of potential energy? t,e/b i k)b8+vngwrv.   m

  A 7.0-kg monkey swings from one branc041hfyqz dp0yjpu4 /rqr*zt mzjlc* 4v.6d (zh to another 1.2 m higher. What is the changzl4jp hyz6q4(fd*rr v zu. /y00dzjtp1c mq4*e in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter cha wl g9.7 g)qczm0-gcgynge if his center of mass rises about 4.0 m during the juq.m0g wlycgg- 9gz) 7cmp?    J

  A 1200-kg car rolling on a horizontal surface hap0.hvetsy*j xz( (mn9s speed v = 65 km/h when it strikes a hzjm ns(xety p(9*. 0vhorizontal 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 th78ey w1j/x(sa4noath e ground so it is 2.20 m above the ground. What is the potential energy of the bosao8ewy( x71a htj/n 4ok relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 7g3nkqoe 5e*h 2xh4f/ji8 zo t1600 m and climbs to the top of a 3300-m peq 7 xnhi 2ket83jhgf5o/* 4zoeak.
(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 verticall8c*d3u,yfaj 1plp.* kp az1x fy next to a ruler. The end of the spring is next to the 15-cm mar 11 ucpda8*a.f*3jlzp ypkf, xk 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 (5.3uc(8p4w np,s am/s) and grabs a vine hanging vertically from a tall tree in the jungle. How hc, p8 (4aupnwsigh can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting39kgmuwy1o9 x from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictiojcct8; t*m mpn+a/2rjnless 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 kine- jy7kd d-lio0tic energy is transformed into gravitational potential energy without the aid of a pole. Wo- 7ydi0kdlj -ith 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 ve/)mb kzj9si2 qrtically upward from the top of a platform with a speed of 5z /) 2jq9skibm.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 tg(3o k6uib dgg36ux3its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give 3o6x3ud6 kt3 gbi(g ugto 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 a +h d3iu(kz1+k(xkug qlong the looped track shown in Fig. 6–39. If the block is to duk3(u1( kzi+kxqh g+remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness co/3sj q.9.v hzca od;konstant k), Fig. 6–40. The block is given an initial displacement od9v.co. q 3/kzjsah; $x_0$ 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 jumperrfkt9td8 drn+358dn d jumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) C+89kt t38 fnrdddd5rn alculate 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*-k+ i(+rgw/skx z iud4k5po u. 6–41 is dragged up to point 1 where it is released fiz* sk+/iud5+w(k 4guo p-rkxrom 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 witd .i:e2vngo j+ twi,/th a 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 be placed at theqcu+ )2m y(iiq 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 spriniiqqcmu( )y +2g 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 lud ;(ik1-wtrbtj:9hcycle 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 dir , werol k0lj7,yh (w5tnmfa 0f81k*sxections, collide head-on and come to rest. How much thermal energy is produced in thil0or5wsfkw1 ten,m0 7jfkl x h8y *(a,s collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a sl;byi1k, se72hhp sc8wide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was geph ske1i 2h, 8yb7s;wcnerated in this process?    J

  A ski starts from rest a.si )xst*wrow7 *xw6 i37hp mo/atsf7nd slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above t(,q.z;g(pmdq g ab q3phe 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 bosf3x3q230gba(u,4 dk kujv +0mk vao punces back to a height of 1.5 m. 3,dgfjuka+va4b m0(s q3x3k o uv02kp
(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.i *3l u9l fwdn np,5k/qwkjvj3. +jmd from rest, is 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 the final3l3n /,m duwkjdq lk .fvp+jni5 *wj.9 speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 pasu+/dvklk2t 0 wses point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what st 2v0wkd kl+u/peed 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 glcx jyp8t)6 q5fp;;b18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a vel54ya kac s7ciwy6+ z3ry light horizontal spring (k=180N/m) as shown in Fzwcys7 +kl46c3 ai a5yig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal sphbbo(;/ug: tzqn: :b nring, 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 :(z /bbuqtgoh :nnb;:beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space sh : in9 d;3vui j9am7v y;ff.2exnit5jkuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landit:7 j nxua ;;iym5.v9fie3vifn 2kd9jng 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 piano to a sixth-sto3, r2jm* dynxd-vuyp0ry window 16.y dj * d0-n,rx2ypmvu30 m above?    s

  If a car generates 18 hp when tr)*l) ytjt(f qfc5zi5 haveling at a steady 88km/h what must be the average force exerted on the car due to f5hytc(ft)*qljf ) zi5riction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is t5 rb5sw*mv 7m+.0 pnlka7kbn hhe average power delivered.hs 07k* ra7bn bp5vw+nm5k lm by the engine?$\approx$    hp

  (a) Show that one British horsep rzaqol,f8 gfjfr6)yq5ds09o), efn6ower$ \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 oz nh-90 r dvwq;n6/tvr+zgeg ,f “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/-x* su*t,w1:grsctv y h in about 6.0 s on the level when it is in neutral. Approximately what poytv-r ,c1s gwx*s:tu*wer (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: w;t(dkap qgt9m(t 9j h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this mot4h: y xmmm+c(wdi+s9h4 u)adjion takes 1.5 s, what average power was dev:mjwi 4+uc s+h4 m)d(dhxy9ameloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through4v og(d5ke4fr a height of 3.60 m. What outpuf ekr54(4gdv ot rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium sta-ouuc y f,js:kmh53kw*ud n:9al48hgirs in 66 s.uwj,kho:g sn:y* h f9mk3ac85 uud-l4 The stairs are 140 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 cyclh-na+n-kx7 )j evq5oeist 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 hill can it climigd;s 8 4 pc+r4n)j)cgo4r mvrb at a constant speed of 75km/h if the frictional forces add up to 650 Nip rrjgncc 8;4m orsv +g)4d4)?    $^{\circ} $

  What minimum horsepower must a motor have ts w.f3p ,wj:pi3tv 9vt0 27-irwwjburo be able to drag a 310-kg box along a lejj:f-, .v w9v03r7twtuib2 w3 swpripvel floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 0xzqn cr- 1z (jo7o,qe7.0 $^{\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 habx f7mb) l aoi10u) 7yzbvz 7d,h9h.sdve 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, bubh 7)0f,libz.7 hd 9 1ybvx7)zaudmost 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 solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground,y; )tk lq5m4ox 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 muchxo k;l)q tm5y4 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’ej7-dw *fnu3 *ek*ry8f. hccbs famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What bef*j8 wen 3* 7yuh-d*rkfc. cminimum 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 withoutb9mj u;a 5dbzjtgjk5lx( /t9* 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 of9d ( j/*mb; 5b lutxjt5akg9zj radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft without his pamx8q* q7m tw0zrachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass wamw8*x0qt z mq7s 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 maro+d3l:w h -cord of length L whose other end is fixed (Fig. 6–43). o:awm-+ld3 rh
(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 climb is madepig/cng94hl4i hmj,q;5k xo 7 in 5.0 h starting at an elevation of 23,h4jp/nkho ; i gxl49 c5qg7mi00 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 28 m above a /vj/ og,fl m1ohuge 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 0t cna4q2goax4+g o4pin California claims that its lifts can move 47,000 people per hour. If the average lift carries people0x q+4tcoga n24p4oga about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam jsi,ymh0irlz w .r 9 s;xd0l)8at the rate of 650kg/s and falls vertically 81 m before striking the turb,d8srm 0y; rls.i9 jxhzwil0 )ine 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 roller coaster wito8r xp9gvcf;28oyib0o 2:jpdt, x hq.h a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the c:yd;p8or09xcgvh8t oi2o ,f2p xq .jb ircular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body couldm)ci)wn (p-x b convert a candy bar directly into work, how high could an 82-kpb(mx )n-ic )wg 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 upward angle of 45obzmdq47tl((uu: v7uo6y, qk .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 0.60 .mn5h5xj f p)dmm, 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 its peak?d xj 5f)p.nhm5    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out o0(ubnnsoj,+yfosp2p(q 5 a e*ver a lake (Fig. 6–45). He releases the rope wpnynosjob(2q 0puaf(s 5* e+ ,hen 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 athlet cy2tegb uw5./r5wuu2ke:us ddo , z *g(v4a6ge climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accompdubyugv55 g*2( edzwwe4uor:., ac /6kgus 2tlish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by reve-dnfwsoy d4wmf+-yz ;i 5 x2 5f0;gdlnrsible turbine0d5o zl5fxd -gfw2ysd f4-yi n ;;+wnm 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. What is the springpyt 5t j.l7pb0 f4kfc,u() zlg stiffness constant for each of the two re7tj5f .lgk f4b(0y,cp t)pulzsulting springs?   k

  A 6.0-kg block is pushed 8.0j.(pz 5oim hdopj prx. 6sbj.i ,1k.+q m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long will i drqni 0 m)zz(brxhw*gy .)w*.t take to accelerate from 55km/h to 75km/h Assume the power stays thei0hny xb.* dgq)zwrm( .w*r) z same, and neglect frictional losses.    s

  In a common test for cardiac function (thaf6m2 5kpd( xe t:: w5vr.3psizlcdi1e “stress test”), the patient walks on an inclinr d(xicw 3z6.5past:: dv2kep if51lmed treadmill (Fig. 6–46). Estimate 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 dist23sp+bw e syn;a6ve qrjz;22uance of 500 m, what was its velocity when it left th22;paru2qe y jse;s v6zn3b w+e 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 8 9ojce)5lq rwldhg ld8, b0m0height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity c,lg b98 )jl8deq 0oh lrdm50woutput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s