Question

Numerical :

A car of weight 20000N climbs up a hill at a steady speed of
8m/s,gaining a height of 120m in 100sec. Calculate a). work done by the car and b).power of engine .

Answer 1

Work done = f × s
=20000 × -120
= -2400000 J

Power = work /time
= 2400000/100 = 24000watt

Answer 2

Work done = Change in the total mechanical energy of the carPower = Work done/time mg = 20000 N ⇒m = 2000 kg assuming g= 10 m/s2 h = 120 m t = 100 s P.E. = mgh = 20000 x 120 = 2400000 J v = 8 m/s K.E. = mv2/2 = 2000 x 8 x 8/2 = 64000 J Change in mechanical energy = Work done = 2400000 J + 64000 J = 2464000 J Power =W/t =  2464000J/100s = 24640 watt .