In what ways is the wfv/ sn; m, jtw3r0rg/yord “work” as used in everyday language the same as that defined in physics? In what ways is it different? /gv ;jrws3r m0tyn/ f,Give examples of both.

Can a centripetal for6lxn /;+h(b;me iq mrfce ever do work on an object? Explain.

Can the normal force on anf: js0kylkykxy4 51n3 object ever do work? Explain.

A woman swimming upstream is not moving with respect to the9qg5 ty4gvpqukb-;.+ u s1yrp shore. Is she doing any work? If she stops swimming qs1u.9py-tg p 5 by uq4v;kg+rand merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: C/aby cgfvn +2ats nl5s8*i3s/ onsider what happens to the dishes when5s 8g n3*sbscv/ al+yitfa2/ n you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even thougf:2m7otc94wl h 3kwcxh you are doing no worlfc:w ow9k4hm c2x7t3 k?

You have two springs that are identical except that sprsqp+y+l)fd4uzbji 9ym+ * rd+ing l is stiffer than spring 2 p*j++sb9l4qyru+ + mdiy dfz)$(k_1>k_2).$ 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 kum,e 4:s;ji yj ;to2xthat is free to slide on a frictionless surfa y ximju4,ot;;se:2 jkce (Fig.6-30). The 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 grav1t yg)b8def vcm ;xk.5itational potential energy change when you jump as high as you b.5dtykmxfc ;1e 8g)vcan?

In Fig. 6–31, water balloons are tossed fro2ei9r l7 oeba1s 0:oecsd g99bm the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impaes 99 :aibs2 97blreoe0c1dogct? Ignore air resistance.

A pendulum is launched from a point that is a heig 1lfki y;+c7hm/.rt;dw uzum )ht h above its lowest point in two different ways (Fig. 6–3/;ly. u z+wthk fmricu)7m;1d2). 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 .xswwlwg g q*):)rv 7otable. If you compress the spring by pressing down with your hand and then release it, can the spring leave the tabw:ol7wqx grv.*g)sw )le? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). Tryy* lxsf;/( /:gy jg5lptg4khe instructor pulls the ball back and stands k*5/rg4ls pj(; lf:ytgyg/xyagainst the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the g.o:)rr0 xgc qrjsw-/ lc;vw3xravitational potential energy when water at the top of a waterfall falls to thejoxlg.v :sr0 r3-c/x)w;w rcq pool below?

Describe the energy transformatioh3nzl* :u 7lfkns when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts skis-ub 8-mhgv1y ing down a hill, but after a time is brought tsgy--hv1 m8ubo rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest am fllu 5usjnj1v3qld xi9;4,3t the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there ij 5qu3mjx nul1s39vld; if4 ,ls no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pate)/6kzago*,r0wc7 *pw ht hhp h rather than stepping on top and jumping down on the other siw)g*0k*pe htz6/pwhhc7,o a rde. Explain.

Two identical arrows, one with twice the speed of the other, are fired into ldanyt8)d9 d) a bale of hay. Assuming the hay exerts a consn8a 9d)ldtdy)tant frictional 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 terms o;66j yevzkr kz:5m ue0em-s5kf energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be me e z5m:6kyvk r;kj6zu-5se0 wound up.

When a “superball” is dropped, can it rebound to a h.aezges6 9)t :e /iltsf0uc8c eight greater than its original heigh6ftg 8.)90cscltsue : i/eazet? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on t8z wh r:ab,14*oaju ubhe suitcase 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) thuaaz8*1bh , ou4r: bjwe height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed ratherd.8zjvm h9o4j than the work.

Why is it easier to climb a mounfbw/q4hhd7cb+9 n9lj zt)9po tain via a zigzag trail than to climb straight upw q/9nph9+d9c 4tzbj b lhf)o7?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes +3eje5y 5 m. 5cw3lmjim;miqsto 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 jiql;5.e mj3iymms 35+cwe m5 for this, using energy concepts.

  How much work is done by the gravitational force when a 26yxg f:/yo5 a8k5-kg pile driver falls 2.80 m?xy8/go5k a:fy    J

  A 65.0-kg firefighter climbs a flight of stjd+ttg (y y ;onp7*j+sairs 20.0 m high. How much work is requis+gj; dpott ny7+j (*yred?    J

  A 1300-N crate rests on the floor. How much work is/xm / bk)5ov,qa 6gosy required to move it at constant speed (a) 4.0 m along the floor agxom) /kasb5 vqyo6g/ ,ainst a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a wiixq7w4u kxfoc fd/i2;+j :*160-kg crate 10.3 m across a rough floor wit+4 ojf2k i ;cxidiw7qw*/fxu: hout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is a0sltp(he ufd,r92l 8.fdw 90twwor m 4ccelerated by a force across a floor at a rate of for 7.0 s. Find the net work dontredw.wuh(l4o8 w0,rp9 29 slft d0f me on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. Hoxwy) mcf-di84.w4b fg w much wi4 -fg4c myfdw.8)bx work is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we migpq6p ughax4 k+*h)k+ pht not otherwise be able to liff. Shou4gkq k )+hh6x*pp +apw 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 37roiridl pvmb4664o-e 7z 5hy.6 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). The y-hi4667 7rlvirb5o4 pd emo zeffective 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 a helicopter oi wi0s fb(cgq1wp d+0/f mass M an acceleration of 0. w10psi g(/+dbqwfic 010 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 dil+iv)l+r 9bxc stance 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, acti7x*(b z bcbu6kng along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x =z b 7*6xckbb(u 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle acts(;p 8uly wsl8m in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecu7n xu82t)sln4 5d0n mcnl6x cmle, 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 .l;(qce+yc, zj7jps aits 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 anr/ o78de. ugk p5a.sdv electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 125y)z7 duc+lq9 tdq17g n0-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exertsb95xp npjy1r+ an average force of 110 N on the byj19r+5xnp p arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) tg kr ld6-j6s(kb8zn /okkj; h,jkn :-yraveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exe kz6j/6r yn;8l-nk kdbojsh ,:jg(k-k rted by the ball on the glove?    N

If the speed of a car is increased 0ow,qm dxji)zn 1hmwl rad,. lw( 1*+eby 50%, by what factor will its minimum braking distance be inc zd,dr*m+ iol.qw(aexl1wwn ,m j10 h)reased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road,,g8wksp3i0y 9a ger. z investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic fricti.9gi803a rwzp e,skygon 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 mas1hrp 79mwu+fb y;yod4s of 0.25 kg 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 plbf7rpm ;4yyd+u1w ho 9ate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straqqz h qoknj x674r:a*3ight up by someone who does 80.0 J of work on it? Neglect aira:rqnz3hx7j qo*qk46 resistance.    m

  A 285-kg load is liftbd, +btny (u1eed 22.0 m vertically with an acceleration by a single cabbt+y nu,1b(d ele. 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 70*ao8x5bc mx in)gn tthis spring be stretched t87otag0x*nm xn )5ic bo store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1. lw)* m alh3*ktxd2 fa8pl1rz(2 m higher. What is the change in potential ene 8 dlt)p3x2 zfa 1la*(lmkwh*rrgy?    J

  By how much does the gravitational potentyry1g2:mi / o3 sixie/n/ ,eicial energy of a 64-kg pole vaulter change /n, /xr/e gyi1iycs2e :iim3oif his 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 wl1hhsasj2fn6 k;l o/*fm:m+then it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness conm:/fkf* htl+12lam; ons 6j shstant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it ij9)dx3 emoux ompt-7(/64yyo pg +pyns 2.20 m above t4n x7m(pygo3yy e/) -9uopp dtmj+ 6oxhe ground. What is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts atb1eeggn ofxr6gq(fb6/x * ben6z,-2 t an elevation of 1600 m and climbs to the top of a 3300-m peak. x6/x bqgnbg( tfe6 o1e 2ne*z,6gbrf-
(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 d5i jx u ko)a1gor4c6xb5+4msjo y:f(hangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.i+k5g xd6y5 )ombu ox(4a 41:jrfsjoc 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 to t+u mu0qmmszu62.qo .p speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How hig u+ o0z2qmu.qtu6sm.mh can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting froumv+s9b .(s g41s+zqejnia m,m 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 sh ;cbhqn 9)lgsw)r+;hguv fv-:ove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformedd:eocr9bcxic g.e1* 84wui1 m into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/sccmr8 e1914igwi oed:bu cx*. .    m/s

  A 65-kg trampoline artist jumps vertically upward from thqw;sk ;m*gvfv78yni/ e top of a platform with a speed of 5.0 mfvm 78n;k; wq*igvs/ y/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 stiftbkf02 ,fm 1 m0ffzhw4fness constant is 950N/m is attached to a table and is compresst4 bmf0zh fkwf21 ,mf0ed 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 along the looped trachoot 9e:wm(-2 eqczv1k shown in Fig. 6–39. Ift1(c:-eo2hmv w 9 oqze 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 be released?    r

A block of mass m is attached to the h0pf3i f70xe(ode)w /)5 owlx *dcmcfend of a spring (spring stiffness constant k), Fig. 6–40. The block is gie)deodmix3fcwf / *(ow7 0x 05cp )flhven 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 bnu,tkfrw;lh). rp h oxh pss((d56e8) ridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assumin) .hh(sf w)xkrh5d ,(e6r;tsop lu n8pg 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 dragged up to point 1 where it izup01y tq .+m,cnyi- ps released from rest. Assuming no friction, calculate the speed at pnim1pyp,y .qu0 +- ztcoints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s anxh cn5 5k7o yll;9oz2t 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 spri).mhc7l jxx0 d:ts5zlng to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the sprmx0z).7ltd: x s5ch ljing, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a d do jdl 2lat(s2i0)vtm16: qs6tlj3b 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 irj ifv 6hfwdud,cxrm(00 fk2mo 81(p9n opposite directions, collide head-on and come to 6m,1 ro8i(fr0d jd9(mcv2wx pukfh0 frest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slor-dbvs kz (9)prn*1,f e ay*y5dtt 7xide 3.5 m high and reaches the bottom with a speed of 2.2m/s How much thermaotf-)v1t*py*d 7esk drx y,9(zrn 5bal energy due to friction was generated in this process?    J

  A ski starts from restp4vjamm2-vhfp: 4l 9v and 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 9qp+kbnb2 k+nj4u*u q 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 boun 4a;1q2f5dndqj xlotz0b),4 frfcr6 uces back to a height of 1.5 mf;fqd c5u 40xr)l1zqa r62ft4j,dnob .
(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 ayk16u hxgij78cross a floor with a constant horizontal 6x17hguk 8jy iforce 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 final speed of the crate?    m/s

  Suppose the roller coaster in Figfh she9)bww 4,. 6–41 passes point 1 with a speed of If the fh9ws w ,eb)4haverage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12aqu7sbw-i ea3 6gio/. m/s reaches 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 is firmly attached to a very light horizontal x xl /bqa.w23tspring (k=180N/m) as shown in Fig. 6–40. It is noted that the bloc.t/w q3 2xxlabk–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 ffaiu)l42ez9x: i9qwc)tw--lh nd nb( *jf 1 jbirmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a lw4xz -ejd(1f w h2u9bbictfniljqa*9:))-n table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space :gudsf*,: ard shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontall:d, rug d*af:sy 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 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-story6agogb xdm;v) crc bm*s;5 49k window ckgav*r ox)csd9g54 bm;m6b;16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the avi 6l l ow2m* yk1z8zmk4baj;:uerage force exerted on the car due to friction a j;*k:z klm 8zuoy26al4 iw1mbnd air resistance?    N

  A 1400-kg sports car accelerates froc (cegviz;kr3a6u8:q3 (/ h :mhixzo vm rest to 95km/h in 7.4 s. What is the average power delivereheoq6u8/iz z a3;(cicvr:( x3vhg:kmd by the engine?$\approx$    hp

  (a) Show that one British horsepuw021ywm 0n-a j+grprower$ \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(ihc(js2 z0xj expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from 6i*yk, * c ahjr57;r7qvv pf th3ftx,kto 65km/h in about 6.0 s on the level wheft37*6p,c ;h7v5ka*t yirkfrx ,qj hvn 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.bzer74hhf a0 10 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-k /k2kj,k):ic0 nhktptg shot from rest to 14m/s If this motion takes 1.5 s, what averag :k2t,k th ki/kjp)nc0e power was developed?$\approx$    W

  A pump is to lift 18.lc 4hhe+bdk,g-ml rx1fi/ :bs jxrt/:4f9d y-0 kg of water per minute through a height of 3.60 m. What output rating (watts) should the pump motor h4fk l,di r-d/e1 hhjx+yl9f4mxb :s rc:/-b tgave?    W

  During a workout, the foot :tcz 8xgk7z1hball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle of 32 7 z:1cgt8hkzx $^{\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 clinuav z,j5 hk1/mb 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 12 )wr*lnajew j3 l9+al20 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictionala) 9l3 w jl+e*nwrj2al forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor zee z9 /;csdoci/o tcn/pm*xb8a/4 3nhave to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictionca9 /ozbcei83 / xtmnp ;/z*co4en/sd is 0.45?    hp

  A bicyclist coasts down a 7.0 dndhlh./bi+qwjq mz 96q6ily;/, sl+ $^{\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 buil b6 sn:nlusghn,d7*) pt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remain) pnnhn, u7g*l:6s sbds 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 firsmq6 i 4srb fh-9cuyrq/mi2/ 9ht shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above tmi/hb 6/9uqi mfrrh2q- c9s y4he previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jgvzj) tvmby : +ga:.hekik9: )ump (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 ak:gztj+a )kh b:m9e)vvi:y. grc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without frict 5 h5 qf51n*oin0d) l1czqqthuion along the looped track shown in Fig. 6qilon0h5zq*1n d )h t5qu 5c1f–39 is to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after ju/t fat.y 3xn*bmping 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. Ay*bttx 3f.n/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 horizonhvj o.vfp38 8wtal cord of length L whose other end is fixed (Figwvfoh8. vpj38 . 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 climb is madekix1 l wz2.*rx in 5.0 h startin* xz1r.i wk2lxg at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above aab) ; :jw;uoya-nv4 (fog/q lg 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 Californii/yf z n(w)oo/a claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) n yfzoi)wo//( higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at t it6qok 6k,ula2w xvbu7l82:ow2x bqzqr45f1 he rate of 650kg/s and falls vertically 81 m before striking t1aq5flkb4766oz2uu xw l82ox v,qqtr :wi2kb he 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 roller c heu9bq)k15czq3 i.te( m d4owoaster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and )ied k14b9u(5ctwe 3qqo.mhz 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 cou j9z2 bxpu*zbp ;jj3:ild convert a candy bar directly into work, how high couz px *;j:ui9jzbp 2b3jld an 82-kg 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 z 6 9xrm8s2l/ybbjc2r45.0$^{\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 m+c0w ezte mb,3m, and it tells you your weight is 710 N. Now if you jump on theb ,m3w0eec+z t scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs qru q6c/*k-43 the yzzat 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is ze4e*y/cu3 6rqz thk- qzro.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9.0 9h 47ntqw voo0)ei 52(dqmnmu uk a(:ns. What minimum power output was used toqoq5km90 an(4 eov n(2id)hnwmtu 7 u: accomplish this feat?    W

  Some electric-power companies u c( 57bzns7kjxagdhs9 +shb* yvh8+ (bse water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoi*ssg8ck( xzd ys5v7 jab(7 h++n9hhbbr. 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 stif5 y0o od6v-vrlfness constant k is cut in half. What is the spring stiffness constan5vor6 y0ol-v dt for each of the two resulting springs?   k

  A 6.0-kg block is pu+7;lis *)us sn opm.,uvtjv ,qc d1rl.shed 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long wusrtc/y77fh jt 1 kpr07h67 i/eqj*cfill it take to accelerate from 55km/h to 75km/h Assume the power stays rft71j sith77y/urch 70fqc* p/6k ejthe same, and neglect frictional losses.    s

  In a common test for cardiac fumj12 ep )jf0c5i hpy6anction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estim 6 a5micjfj02epyh )1pate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance ot* .j,-(whnck l7hq2gx7xo ybf 500 m, what was its velocity when it left the volcano? bh7x.otykng- cwx*l,7(q h2 j $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a height of 2.5:pw mh3p 8b/awxy,d h0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum powep,/h ahxwdwy8m 35:bp r output?    W
(b) What is the speed of the water as it hits the wheel?    m/s