In what ways is the word “work” as,ryi1i361gqn pf 1flm used in everyday language the same as that defined in physics? In what ways is it different? Give examples1m1 qg3y1i fpl6 f,rin of both.

Can a centripetal force ever do work on an object? Exaav 0.i/ ehhw9plain.

Can the normal force on an object e4wb-qk xo / qj,(fx0vkver do work? Explain.

A woman swimming upstream is not moving with respect 2+fa7cb ,elrp to the shore. Is she doing any work? If she stops swimming ae+ b,2f7pcrland merely floats, is work done on her?

Is the work done by kinetic friction fowz,;0o :4atvwke9 hn; 4ylq wtrces always negative? [Hint: Consider what happens to the dishes when you 9;wtqwn;0h kv4z : ,tyl o4weapull a tablecloth out from under them.]

Why is it tiring to push hard q20; :hrekkhz against a solid wall even though you are doing no work?h; hkz2re: qk0

You have two springs that are identical except that spring l is)z1r kh4a0c .t 76zny voh+mrm stiffer than spring .vz4 trhmyza1h7c0) 6 k rmo+n2 $(k_1>k_2).$ 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 const1fs-2d7b(ysbx;cq1. ghj a tsant horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoihx jy2sd s1s1a(bbt .g; -fcq7nt A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potentidfmolyhk c1 k);nbh7f05(h 6hal energy change when you jh5f); hk(fyk m6c0b1ld ohnh7ump as high as you can?

In Fig. 6–31, water balloons are tosse- dz6ascb 6xq -p5-b,uc3txnbd from the roof of a building, all with the same speed but with different launch angle3 6 pxzsubt --abc,6nd-xqc5bs. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point inl rdd qnj/klj n7jat.2r3s+02 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 initia+tar d jknr 7sq22.j/ljdl3n0l 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 com7/ gwg tjt/yyf*sr1u p iiro.9:4 nx* )vvyeg6press the spring by pressing down with your hand and then release it, can the sprin9/*t 7rnyigwvx yeog6*4jut. gif :vp1s)y /rg 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 instrucrvi.v c;swz nh8yy7,*tor pulls the ball back and stands against the wall with the ball against his nose. To avoi7n*w hvv,sc y.zyr ;8id injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational p l*,kuds 3 yp;fwp:eo,otential energy when water at the top of a waterfall falls to s y3kpdp:* o;,u,le fwthe pool below?

Describe the energy transformations when a child hops around on a pog ze -,so h;z;86*ks:m bht8c f3kyxqkao stick.

Describe the energy transformations that take place whe7r6+xq qdcch7lun r- -uar+r3n a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdrxr a+ccqrqu -3 r-uhld76 +7nrift.

A child on a sled (total mass m)c fes-8t qgf: 5v2cq6nw y*k5b starts 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 there is no friction, and (b) there is friction (deep kf2q8 -n*:tec vwgb6cf5y5s q snow)?

Seasoned hikers prefer to step over a fallen log in their path rather th t c,: -*2d ehbcden-f/yu3tssan stepping otds c nh-2 ees-/,3yfd*cut:bn top and jumping down on the other side. Explain.

Two identical arrows, onftn, fo6 hm(. +bjt6qge with twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrbf.ojt6gtm,qf h( +n6ow? Explain.

Analyze the motion of a simple swinging pendulum in terms of +di5)odzv3p jenergy, (a) ignoring friction, and (b) taking friction into account. Explain why a 3)p+ od5 dizvjgrandfather clock has to be wound up.

When a “superball” is dropped, can it rebound +5ziy5otksgawmm d7f;5i 38gto a height greater than its original height? Expa iy3 m+w5got5mg dski7f;z85lain.

Suppose you lift a suitcovwor4 09 ojj9ase from the floor to a table. The work you do on the 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) the height of t0jor9jv wo94 ohe table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the )mjv5 cxr6l uk3f9q/c work.

Why is it easier to climb a mountain,5/*wxbanthb via a zigzag trail than to climb straight up?t/h5*, bxan wb

Recall from Chapter 4, +02f ij u0,zej7vxxar Example 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, z0,x +f7 uiejva0r 2jxhow much rope must be pulled up? Account for this, using energy concepts.

  How much work is dony) *1k dwpd3l ,iuk8xre by the gravitational force when a 265-kg pile driver falls 2kkd,py d l8*iw)xr3u1.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much j x++8kbdb2 4h pzva(qwork is reqph+ (8dabq +jk 2v4xzbuired?    J

  A 1300-N crate rests on the floor. How much work is required to move it +kejw .vy02ylr.ombi,uv 3kd - 69rqt at constant speed (a) 4.0 m along tower+.lvbyj.-6 utr q,2kmki39yvd0 he 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 160-kg craq :. cjwlapah)d)qn 2n q.m.c7te 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was np.ccq. d)jq am7 l2n.):q ahw0.50?    J

  A box of mass 5.0 kg is accelerated by a fz3; nm w)9u*y jqhc,oyorce across a floor at a rate of for 7.0 s. Find the net work done on 9juo)n,* ;ywm yq3hzc the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fla 4o8bh/2qeprqrfytn(5. l;/olq iie0t on a table. How much work is required to stack them one o5iq0t2q p/ /eoirr;b.ehll nq(f8o 4y n top of another?    J

A lever such as that shown in ; roa. w3 +rmf)m1rmwtFig. 6-35 can be used to liff objects we might not o mw t+;1w rr.fam)m3rotherwise be able to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3xh ep(6bcp(e;.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 effective coefficient of kinetic friction is 0.40. Calculp (pb( chxe6;eate:
(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 of mapoo1bv*qk f24ngw )* qss M an acceleration of 0.10 g up4* o2vkq*1 p wf)qbgnoward.    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 sn6w7-z . r ftbjb;uv3a.un ,glinear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown rx7ls uo )7a0nin Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to xs 0 )ar7loux7n = 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 acts11wf7 rkilzur,pya1m- sbn j/m ln02:; y.njs 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 molif )* (nefj zpk4zk(,yecule, 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 tiao4-g :c0hyr 63 4rkb .ka8jn3vrfywhat 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 electron fc2ad5m cou*7tofgc8k 8 ui )8$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-kgcar traveling aun - wam;thkg7od56:6cr0fizt 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow wh6elg,tuy) z g.ose string exerts an average force of 110 N on the arg,zety )l. gu6row over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 c 7+ qlfz;t 6zq5c+kbd8;yjoyc m when the zcql f;tq5 +8ky6 zj7+ocyd; bball is caught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minix993 ktzncurol,*2 ; d quny*mmum braking distance be incre, 9*z3nxqy 9octkd;u*num2r lased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark t m1cfs o)-rlw4o be 88 m long. The accidefwc m o14slr-)nt 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?)    m/s

  A softball having a mass of 0.25 kg is pitched at s3x4e2mqd bwoqm65(b By the time it reaches the plate, it may have slowed by 10%. Neglecting e(dm6 wb4qmbo q352x sgravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if t; ..zt3g jckwsc+wnm2hrown straight up by someone who does 80.0 J of work on it? Neg+ 2.tm.cw wkc3jsgz ;nlect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an aco rdyw w52q:0:tut2x .doo7gxceleration by a single cable. Dete qxr.yd2: wt:w02t 7 xouogd5ormine
(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 constantt1o gbk41ynrs((9ntxhdr s27, k, of 440N/m How much must this spring (9o1nh t7ysnt2s xbr4(k1drgbe stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to a:: vi*zloqp1ex aob;* r,hi d6nother 1.2 m higher. What is the change in o, il:ie1 dpvx* q6:;a*o brhzpotential energy?    J

  By how much does the gravitational potenm+t5k86lz ow xtial energy of a 64-kg pole vaulter change6 wmlo8k+z5 tx if his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizkx.xaax3 - n2hax./ n. /jfnyjontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought t xxnn. k-x/njfj/ya.a.3xah 2 o rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m.vwma8f8 l h:fao/mb+ xg68vd above the ground. What is the potential 88dl xov:/v a ff6 mah8w.mb+genergy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to th*vwn)a. 5htf +rt4 fkne top of a 3300-m peak. nh)+.t5kf f4t wv*anr
(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 v(zof2m t)z4g qertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5mf oz z(g)2tq4-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and 1ywyww-ajw 2*f+a i1w grabs a vine hanging vertically from a tall tree w+a yjww1w* wfi2a1y-in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless hpox y)(w5q0vca3wd5 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 giv- u cppb3ins6z9. men.en a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinets kz66o7t n.p3a 5amsric energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leassz6a.o 56t n7p m3arkve the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upe u dbv8(jx3j/1t6orp ward from the top of a platform with a speed of 5.0 m/s. j(dpjt/8b13o x v re6u($\alpha)$ 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),u 9jt1je wu9a 0pn,6qo 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 to a 0.30-kg ball when releas quj6 ,n t09oauj1w9peed?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides wox5iwuz/q pjw1:f.zuxk: u9 7ithout friction along 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 rad uxj/7kfq wxw 15z:i.9z:opu uius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the 1wvt p h33ssb3end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displacemew3t1ssbv3p h 3nt $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cor;j 5.jg)dqk z 0qcbrs*s)iru 1wzb-u4d whose unstretched length is 12 m, and falls a total of 31 m. - d;4gi jubwbs)k.ucq0) q5* zsrrz1j(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–o ((,dnmoeu, mjikw2mj7,ll341 is dragged up to point 1 where it is released from rest. Assuming no friction, calcuow o(dn(e,lju,m,km7j 3l 2imlate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a sprq o:qq 8pqy0/eed 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 design( bmbj , +z9gemoz26gking a spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when thbj9 (o,gzkmb+z 6egm2e 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. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7eb5li:ayypy2 ny( 2k4i s.pwa.j.f;g.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 trpn7tfox);a:y g ) urmt3j5ax4o7 9hznaveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal en n;jtgx4uz7o3a7 ) h)m:5o9 y pxatfnrergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m hig,kfnu6/ *qlwiget*l 0 h and reaches the bottom with a speed of 2.2m/s How much thermal lt qe*fwlg0ik/ , u*n6energy due to friction was generated in this process?    J

  A ski starts from rest and slidesf7 k8aooa:c q 6c+qks+ 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.e8zn tgk/*xx3hw+su2kze7b - 0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1ijaqy f.i vve;+; j:;w.5 m .vey;fwvjijiq: ;; a+.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constmbt)pu 0h w:qchr 3v dg03w,r2ant horizontal force of 350 N. For the first 15 m the floor is friction)3rwtqp ruv h0203 wdm g,h:bcless, 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 of If th74 9mjf jqm;-ivb1qpd f;p p/ie average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveledm7 i4q/91pqjdpf ;f ip-m vbj; is 45.0 m. $\approx$    m/s

  A skier traveling 12m/sy1h dp,d25 bpa 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 spring (yxv rr2jyn0kd).vc 82p r3rs/k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm c jprr)3k/dy.v x082r2rn ysvbeyond 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 sphx8 ny7 k8amh:dr*(d rring, Fig. 6–40. The block can slide along a tabm8(hadhn d *8xrkry7:le 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 shuttle used a “glidt73g 6kjsbf .ier” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence f6bit37jk .gsof 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 taktci j1jdiy t1i 1tv0(c/0 izm:e a 1750-W motor to lift a 315-kg piano to a sixth-story windowtc1t0ji :d11tiyjzi 0v(i / cm 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must b7jo)e9 -:m/ chbxsa,n gs1rfk e the average forcecefsx,9 mr-/ag7bh 1o)skn j : exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerl9uq;gndzk 0gk 2mr(m4b )pwx4 t.k7kates from rest to 95km/h in 7.4 s. What is the average power delivered by tuknk (07 4wkb2lr4k)gm.q;pd tg m9zxhe engine?$\approx$    hp

  (a) Show that one British horsepowesvq 1nw*n/v+- bw0no 82uohtk r$ \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 .2 c1 cdkxixh; ygg6s.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/hspkj4v(rct 3 z-.* 71yk)iwlonr.-n*q yypjp in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to kep ntsppqko*jry.nzy4 ) i*1-v (r l7-j ykw.3cep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motorp, jp6,s*.l hmq 1jcxr do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If thi ux.r1rjdi p4:s motion takes 1.5 s, what average power w1juri.d p:x 4ras developed?$\approx$    W

  A pump is to lift 18.j.fmne a(dde;0cn; nqrw* 5 b-0 kg of water per minute through a height of 3.60 m. What output ratee qnc 5bddmw; aj.r*;(f-n0 ning (watts) should the pump motor have?    W

  During a workout, the footbag,;5/v( myfwtmz8 x g bcu6q-kll players at State U. ran up the stadium stairs in 66 s. The stairs are 140 mmfgtm z6(c;ukx 58,/yg- qwvb 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 clx9; e7iyjalct22lt( himb 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 rp;c)1d mgkfkc k( zy.c) 7p7fcan it climb at a constant speed of 75km/h if the frictional forces add up to 650 cm;)cydr7c7 pfkk g. zfp)1k(N?    $^{\circ} $

  What minimum horsepower must a motor hoj3l1g7krj86n tj, upye y0g5l:1pu km 1xu1c ave to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if t0 y,nm5jyl c r6luj 1 kgu1xkg1e78p31:ojtuphe coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0hm n .;ehrpd.1 $^{\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) bum026a a/8zce ovxup4yf pers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h2vz oye6 up a/40xca8f If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and 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 qeyl v)z0 zhr83b*/n goff the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one8v3 eh)*g 0b/nrzyqlz. 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, wi-jh uz5:us’s famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m frouj zsiw5:,u h-m launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction al* va 4f2jcow)yax 2gl;ong the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very to)o24fc ;xj ay2 v*wgalp 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 a7vhsz b kv h,1g w-u8i e2whh-qy(9cmu( pu95lfter jumping from an aircraft without his parachute opening. He landed in a snowbank, cri uh( lzs8,9mh7w-kb1yvh pq 9ec5hv ( 2-wugueating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end izznn;ne05n 6f:dbd1zws-u v(ub.hv9 s fixed (Fig. 6–43). (6buzs;n:5 en h. vbd0fzz 1wn-dvnu9
(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 mount:xpq 5ksl9z9j85f rn lain. The climb is made in 5.0 h startingxln5s9 l fzj5 8p9:krq 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 afw+ciwfo2 -9ee 9b.oibove 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 clyv+/fql7- ci +5gbhsvaims that its lifts can move 47,000 people per hour. If the average lift carries people aboutilbcqs/y-vhf vg 5+7+ 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at thsy; )z 1jylzo. +:uiboe rate of 650kg/s and falls vertically 81 m before striking the turbine bladej1.oizyb: +)yu;s z ols. 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 with a circular verticaueqvr)v: 6 +ssrr7h,il loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t deer huqs:v+6srv i)7r, pend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a c6 dl(*vr fuzv/andy bar directly into work, how high could an 6dfrl uz(v/v* 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 6t 39 rqj:2ol kum3w g-;qa4;q gaqzxdat an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compreh- ua, dta)jx,sses 0.60 mm, and it tells you your w ,xja-a t,d)uheight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fig. eb-1n4kknb(t)wktn ln (xi:h5)zi b ;6–45). He releases the rope when his velocity is ;- 1 ebh(k (nn k4)) k5bltx:nnbtziwizero.
(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 cligf2po, o 5xqbt2d,cv4:,0hwd ba r qp7mbs a vertical distance of 5.0 m in 9.0 s. What minimum podr 2pqob p0qb,,4 dfwt7hvx2:o5a gc,wer output was used to accomplish this feat?    W

  Some electric-power companies g;9jz a6 6bv/( lveyupuse water to store energy. Water is pumped by reversyau6j(v lv6zp/eg ;b 9ible turbine 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 sprz,bcvf4j oc13 ing stiffness constant for each of the tob3cf4j1 vcz, wo resulting springs?   k

  A 6.0-kg block is pushedoslt 7q44zq j qqo0-y. 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 xhsjojd:kg d y 47(u3rs,j6o7 s, how long will it take togro:u 3kjj6d7s(j ,4d xshyo7 accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks+.vz;i)t-+vc.5gc qr t czehj on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping .ih++ j-ce 5 tcg) rzqvcv;zt.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 a144;fh,h hv bv i0-i4qtkclmjmpt8 l 6. x/rtq distance of 500 m, what was its velocity when it8p 4 1f0 civh l x./m4q-qmkji,4rth;v tbhlt6 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 wheel from a height of 2.0 m at a rate of 95kg/s lx53h1 ;nh,clou5lg e(a) If this w1g,x u5l; h hl3ec5onlater 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