In what ways is the word “won:ugg3v5lb ,b8 kuo p+q* ly*irk” as used in everyday language the same as that defined in physics? In what ways is it different? Give examplesoulu3q*n:g8blp ,g + 5kibyv * of both.

Can a centripetal force ever do work on an object?3y y wg-m0w08-::ywjwqvyeww Explain.

Can the normal force on an object everw 6 b/t-6xg(h;pv sar3kgol8k do work? Explain.

A woman swimming upstream is not moving with respe4zoouf o2;cn* x+y a1vct to the shore. Is she doing any work? If she stops swimming and merely floats, is work;c1 on2y v*4 ouzoa+fx done on her?

Is the work done by kinetic friction forces always negative?g y mktc )4c8v2v4lzz6os4 r,s [Hint: Consider what happens to the dishes when you pull a tablecloth ou 44,z6ykc ss)4l mrvzco vg82tt from under them.]

Why is it tiring to push hard against a solid wall ev8 o tieqnz68nyp46,a xen though you are doing no w ,yp tozn8x8 64nqea6iork?

You have two springs that are identical except that spring lo s-( 7ig vbytwz2d9tq3n0z m3 is stiffer than sprins2iyn vmt0zz-d7(wo9 3g3 tbqg 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 of- jskh. i0l1fcf-s6txbv( 7on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, anssf 0 hfbi.o1c7ltj x -6v(kf-d 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 yhe yseuxm2; 31 ja(v3zour gravitational potential energy change when you jump as higxhsu1 e(j vz;y23mea 3h as you can?

In Fig. 6–31, water r4blsbr3h-*sa *bnx i )ad 9h(balloons are tossed from the roof of a building, all with the same speed but si h9d*n4b)rr- (als*x3hbbawith different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a poi*(kc/hhb7drd: qn ji (nt that is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial spe/dqk cjdh *n7r:hi(b(ed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you c quu 4fg.,fqw*l0y+cyompress the spring by pressing down with your hand and then release it, can the springlfwfy0u+ ,4y *gq .ucq leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The x vg,h r;; hen4f*zlg8rq w8*binstructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to releas*4 gn,evbh8g*w;;xrfr qzlh8 e the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top x v k-mqxku*abf c.+4(yq4c*lof a waterfa44m kc .*bfuxvc*( a+l-xq ykqll falls to the pool below?

Describe the energy tran-81twd2 i2o2 s iqbnprsformations when a child hops around on a pogo stick.

Describe the energy transfta k5ui+rk8rv (+o wr8ormations that take place when a skier starts skiing down a hill, butto (ri +r8v+wkk a58ur after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) sta2i49 nm9dh ag: drgsjgh+y9h0 rts from rest at 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 the09d9hgj+mn2 iay h:g s9rgh4 dre is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fltmw +6(viv (tallen log in their path rather than stepping on top and jumping down on the oth( ( m+lvwvi6tter side. Explain.

Two identical arrows,q w0rrq*q)/ jx one with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constanqwjrqq) 0*x /rt 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 )3r,(knyd rmr pendulum in terms of energy, (a) ignoring frict(d r3 )ykrm,nrion, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, 6zl 8/ bd 9gaxbbxm cj930stm7can it rebound to a height greater than its original height? Explain.cz b txx/b69gb9m7lmd08a j s3

Suppose you lift a suitcase from the floor to a table. The work you do on tuq 5dlz5xom3r jvv0acq++ cz6q2t1r5he suitcase depends on which of the following: (advz65mx5 rczlq vu21r++a j3q 0q 5toc) 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 rathervyhp;2e;:qt2 c jhy( o than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb 21gya)u+nl;yqs 5l wbstraight up?1b;l5+y sg2wlqy a)un

Recall from Chapter 4, Example 4–14, that nqxx4hn -ke46./, :hzlr p mzq*fs3zryou can use a pulley and ropes to decrease the force ne.ps kxfq-e:m ,*h /z64nlxq4zz3rrnheded 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 wj2: i)7 57wgafpm hkpby the gravitational force when a 265-kg pile driver falls 2.80 m?pwhjpam :fk7g) 25 7iw    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 ntp-g6d+ws w9; bl yx0m high. How much work is required?tnsw;y9+wp6x0l b- gd    J

  A 1300-N crate rests 20(hicopens 8 on the floor. How much work is required to move it at constant speed (a) 4.0 m alongce028n psioh ( the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160ea*.pia x zp44-kg crate 10.3 m across a rough floor without acceleration, if the effective coef.xap *aizpe 44ficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across arnv0hc;mm: qww - (d4p floor at a rate of for 7.0 s. Find the net work done on the bw:cmpq dn -(hmr;v40w ox.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. H lvug3(k2s td9ow much work is required to stack thg2vt(k3 lu ds9em one on top of another?    J

A lever such as that showkn24-v n2 z mjn-l cmjl8p)bu2n in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratijp2-j vb8nu4m n)k22 - clnlzmo of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m dogz:/mh l3pwc xz/f2*iwn 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 coemzwx3/lhgzp2/: fci* fficient 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 helicopt er 1.85/kq;ar4qlylq8vkbra2h +tkh er of mass M an acceleration of 0.10 g upwarqy;akvrkq5h alr+84/ b . k2 e8hrq1ltd.    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 linear and that 6o+z+x3vk):i;x gnbe*io r lm$d_{\mathrm{A}}=10.0$ 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, mo,lm7y./ppq :/zozf acting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the objz qzmy/ ,pomolfp/.:7ect (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 parbx uala,6ers q x/4;8iticle 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, an oxygenxff,su95x,q5 bqgx,l 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 doubletxq*xl(t1o3 w 7zez l6 +cuju6d, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to*4( )uzy5h a8mjzvwsi/qw(q u stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcqu qk s4v,yk s;1p8n x7d1*izhar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired m jz,ju4 q+jqqff7z,3 from a bow whose string exerts an average force of 110 N on the arroq f3 j+,jq,f74jmz zquw over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) /kzlif-i7s +ieh w /z1traveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on tf-zi7/lie1k h +zi/wshe glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum bragrby1gs + u+ a/x igu5*ti22jiking distance *5istg i2/ya g ux u1ig+r+b2jbe increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s sppxd-4/c evswq. v19 gkid 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?) -psw 1pd/49 .exvvgcq    m/s

  A softball having a mass of 0.25 kg is pit tzzq4)9d o+:4gefqikched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force +fq t:44goze)i 9kdq zof 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 goa(;f4+ dluz )*u oew-tqimi2 m if thrown straight up by someone who does 80.0 J of work on itut;i-i2a *fo+ wqzeum )d(lm4? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an yv8a;nu dgr7u)d +j-1-ae v 4wh)zhmoacceleration by a single cable. Dete dhwmv4jg ea vd u8r);yz7ha+)u--on1rmine
(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 mug(, d( :w qlahm4 8ajhwmu.hg;st this spring be stretched to store 25 J of pml4u whq (mh(gha8gd.:,; awj otential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m highej +*m2twlnr(fr. What is the change in potential ( +2rwnf*jtml energy?    J

  By how much does the gravitational potential energy of a 64-kg pole vaultll/o2(muz5 /c 5q ubguer change if his centum2b5gz(cluq o/5/l uer of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 6*9uh4septb 6ecmc82d 5 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffnes4 um 29ehe d*ct8b6csps constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground/ h-xl-fe;gadmm r0k* so it is 2.20 m above the ground. What is the potential energy of the book relat*;fm-h-k max0 lgdr/eive 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 1600 m and climbs to the top of a 33*d *ti/o4+mbku58x7plekzi jk- 8b k i00-m peak.8kk7 *e5 /i-oju4d 8 z+pibkxik tm*lb
(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 zz9c3wv n/ jy5cw( zip0lw60n the spring is next to the 15-cm mark on the r 9nw/zl 0cpwnj0czy5 6iv(zw3uler. 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 sgdx s mb,np*1, 15tldzpeed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How ,gdpsb*mtz,d1 x5 1nlhigh can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting fbbe2dhqe b8vh; 2) y8jrom 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 frictionok/ 9*g kdivr:less 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitational pof2v cj0ims )y1tential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of masjyim)c20 s 1fvs 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top/ c3j u51 yl*ripglw,s of a platform with a speed of 5.0 5*/wsrllp 3iu1cy, jgm/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 spns+w+ dgodl bl521(p wring stiffness constant is 950N/m is attached to a table and is compressed do d12(+wobnl5+ wdgplswn 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 i/ g k-(w7 9bqols+whxkq7lg ,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), from what minimum height h must /9i(lo+lgwhx q swq,g-7 7kb kit be released?    r

A block of mass m is attached to the end of a sprin w z *;lsvnf+ppt,ut20g (spring stiffness constant k), Fig. 6–40. The block is givlv t ,tpfspz nw+2*0u;en an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to -ar*tz(+f t86 anuir na bungee cord whose unstretched length istauntf-i+8(6*arrn z 12 m, and falls a total of 31 m. (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 dragmp.x.ur/l r6(uw/lzjmd1p o 2ged up to point 1 where it is released from rest. Assuming no friction, calculate the speed lpl(u./m x o/6pw2u. zmr1jdrat points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 1. pieos32jci .9ih gyd66blp82 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 the bottomkt57bu nq(gwz 85as1k of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Le7g18 aus5w5( kbn tzqkt M be the total mass of the elevator and passengers.

  A cyclist intends to cycleg+q4 -r:ap l2i:y 7fi mh8zsqp 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 d5/gupqcf-h n68bpot uzny0 x+,0q:i/h in opposite directions, collide head-on and come to rest. How muc6i0p0f+b y,x gn cuotq5 d puzqh:8-/nh thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m )sa5p hn5( zmu)bq(z dh/bp )shigh and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generap/spb hzn)h ( mu s(aq5d)b5)zted in this process?    J

  A ski starts from restf9hn o2 -wpuu4 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 m 5m5dxe-2o ig61zvariv x67wi 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 to a height of 1.5 m )h6yp9 flxud/uf)yd x6hl /p9.
(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, isrv c 2(j6c 8y;kn :qrbdme,k7b pulled across a floor with a constant horizontal force of r682bkkvcb ;y (e:m cqd,7jnr 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 Fig. 6–41 passes point 1 with a speed ofdg9j/p5w( rt fs(r ;qi If the average force of friction is equal to9s/ (p5wrqi;tf(gd rj one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a steady upvm.5r7 epgt r8ward 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 attacb rgh-mpa c) yacr/y028 8d*qlhed to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted th q0)ycrrgh a / la8b-cp2d*my8at 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 w 3 b4-24l(oao 4 3vyzfnzenlxhorizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compressov n23 -4ny4x lezobz fl3wa4(es 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 shutdwbx17soolk 56 mqj- 7d v cy.(czb1(dtle 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 landing speed have been in the b 7cojw(dd1ozsck(l-dvb. 1 7m5xq6yabsence 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 19 pg xfzf8veme/:41je9g2aojr 3y8 do 750-W motor to lift a 315-kg piano to a sixth-story window 19jfofd3 evzxap82m ey:9/8r1e g g4oj6.0 m above?    s

  If a car generates 18 :-)bgf r,i *2dpp fyhr2r3tzl7u f g9qhp when traveling at a steady 88km/h what must be the average fidzf-b3ht u7gp :qry9f*,g r)l2rfp2orce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates vhh3+k5k xpf i1j ,q7zfrom rest to 95km/h in 7.4 s. What is the average power delivered by the engine?7,hk1vj xifhzk q5p+3 $\approx$    hp

  (a) Show that one British horse 5-4mnxph gm jzaz.psyn7l8p*20 j2 uhpower$ \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 a vt.v d*b4h r5)o09gduti m6 m4+ibbgure often 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 to 65km/h9t7g+m:d*t+oc7z6yyueq n7v 8kij/+ os qhop in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the cazi t no :6hopyq ++j*8oy/k7u9tvq7m7s+e cgdr traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motoe*zn j2bv og:4b9izf8 r do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest bwe1 acp+x(lte1mlz .6j /j(c to 14m/s If this motion takes 1.5 s, what average power was dmw 61e./+ pleact(1j( xcljzbeveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throu r,eazpz qy+( 6)yr-rbgh a height of 3.60 m. What output rating (watts) should t zyrzp(,+r a6)q-breyhe pump motor have?    W

  During a workout, thesgr53aju4e -xh 7z3ka football players at State U. ran up the stadium stairs in 66 s. The stairks -zjg547r3aeu3xha s 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 cyclist climb 0y (/tzudch b+l)2.k8 uxbgso 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*h a) sj0t- m/+nvdi 7yyh87 ji6vggea hill can it climb at a constant speed of 75km/h if the frictional 8 + 6 vyvam -/ghjn7tj)eyg7ii*s0ahdforces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be m6t njvxfead* a t3:+6+wvu 7be0oyq :able to drag a 310-kg box along a level floor at a sp0bonjeaa+7 t vvf qy:+6udte6:x*3 mweed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dow cky ps061was.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 “5mi/h(8km/h) bumpers” tha0++kagg*e* .9xrp v svho, 6ea 0jwgxtt 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 spokg+6 .r +pxhvsge 9vwa,gx0j*t e*0a ring 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 shet oia-fpk+66blf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, hi-tk6p fbo +a6ow 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 (Fig. 6–42) in the 1936 Olymp7 xvyj/+ut)a,tzqd mp6pfs 7w 6k5:maics shows that his center of mass rose 1.1 m from launch pointw,jtmp q :pa5 m+s)v7kfx7dyz 6tau/ 6 to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding withou;/u 0k1kzml+ o6zv kglt friction along the looped track shown in Fig. 6–39 is to remain on the track at all timgl+v;k1z ou/ 6kk zl0mes, 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 jo i,9 n +w,ur1yvlx2p.3yzkeafter jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assumirok u2 v, yjl1ewy.9+zx,i 3pnng 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 otzlzh:e*u 1.5fdgl 9qvher end is fixed (Fig. u 9hgd* zqlz1:vf5 el.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 tmsjd4n eh7*zee6/ng :o the top of a 3700-m-high mountain. The climb is made in 7zeh*es m 4gje6:dn n/5.0 h starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg ejxvmn.g ro)*m.i o 1+tlevator 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 its lift)bc q1wcg u79bs can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power neededwq1c )u79gbb c.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/j c; 0h4t6 b s1f:ssf 4(v+8dmqddqrwss and falls vertically 81 m before striking the turbine blades. Calculated(j1; 86shfsbtmssqv4:+4fwdr dc q0
(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 co5drrn7w,u7x cw; 9x k9z3qdhsaster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is a k9udhdsnc;5r 3xw 7z,xr79wqbove 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 could convert a candy bar directly intogj00 (tpspp6 u work, how high could an 82-kg mp0t(6up p js0gan 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 of0a6sxoe+gx0d )ue x1t 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale co tajts.ww(q, j+ow5w9kb /a m o5beh61mpresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale wj1qwt e6kbb w9/,5a(m oat5+ wsh.jo read at its peak?    N

  A 65-kg student runs at 4fu4yfgxq 3,zc l,zd5 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velocity is cgq5lu,xd3,zfz4 yf 4zero.
(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 9.0f x+um36mp-j9 v0sszxq (h2ae s. What minimum power output was used to qh + m96u3xspse-ajx(zv2f m0accomplish this feat?    W

  Some electric-power companies use (/ n,rbgop:osdlp1ew. 1ma 6nwater to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in (pasb1wo./6n:1mdp,n r e ogl1.0 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 ik-lvmqf9 b5c6 n half. What is the spring stiffness constant for each ol5bckm- 9q v6ff the two resulting springs?   k

  A 6.0-kg block is pushq;hqor( u je. nsd3xu11x(/eded 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 b10 sh2 6 , r6oi)fms.zi3 kdqwonn1rglong will it take to accelerate from 55km/h to gznd6,w 3iq2. rf6)ro sh01mio ksnb175km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress t yk- ugcke (*ojmtu9-wr*8bz +est”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the tr *9r( juwkyu+-- eb8mo*gtzckeadmill 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 u4+knd6ud / k0fw:z/ xekfn i-bpward a distance of 500 m, what was its velocity when i 0k+d6zd xi4/u:fe/ wf-nb knkt left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water a9nbyz e4ckx;*ho2x.l mp r ee 6a0n,66c8riv wheel from a height of 2.0 m at a rate of 95kg/s (a) If this wat ax6 4c2pinok60 nm9 ;y.le zh6re8ce,rxav* ber wheel 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