Physics CH 6 CLSSWRK.pdf - (6-1 A 75.0kg firefighter climbs a flight of stairs 28.0m high How much work does he do F=mg=(75kg(9.81m/s˄2)= 735.75N

# Physics CH 6 CLSSWRK.pdf - (6-1 A 75.0kg firefighter climbs...

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(6-1) A 75.0kg firefighter climbs a flight of stairs 28.0m high. How much work does he do? F=mg= (75kg)(9.81m/s ˄ 2)= 735.75N W=Fd= (735.75N)(28m)= 20601J (6-3) How much work did the movers do (horizontally) pushing a 46.0kg crate 10.3m across a rough floor without acceleration, if the e ff ective coe cient of friction was 0.50? m=46.0kg d=10.3m a=0m/s ࠵? k=0.50 F y=ma y= (46.0kg)(9.80m/s ˄ 2)= 450.8N F x=ma x= (0.50)(450.8N)= 225.4N W=F p*d(cos ࠵? )= (225.4N)(10.3m)(cos0)= 2321.61J (6-5) What is the minimum work needed to push a 950kg car 710m up along a 9.0 incline? Ignore friction. W=Fd= (mg*sin ࠵? )(d)=mgd(sin ࠵? )= = (950kg)(710m)(9.8m/s ˄ 2)(sin9.0º)= 1033819.64J = 1.03*10 ˄ 6J (6-10) A 380kg piano slides 2.9m down a 25 incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). Ignore friction. Determine (a) the force exerted by the man F =0= mg(sin ࠵? )-F p=mg(sin ࠵? )= = (380kg)(9.8m/s ˄ 2)(sin25º)= 1574N (b) the work done on the piano by the man W p=F p*s= F ps(cos ࠵? )= =W p= (1574N)(2.9m)(cos180º)= -4565J (c) the work done on the piano by the force of gravity W G=F

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