A van of mass 1500 kg travelling at a speed of 54 km h−1 is stopped in 10 s. Assuming that all the mechanical energy lost appears as thermal energy in the brake mechanism, find the average rate of production of thermal energy in cal s−1.
Mass of van = 1500 kg
Speed V = 54 km/h
= 54×(518) = 15 m/s.
∴ Total K.E = 12mv2
=12×1500×(15)2
= 750 × 225
= 168750 J
= 40178 cal.
Loss in the total energy = 40178 cal.
In 1 second loss in the total energy
= 4017810 = 4017.8
∴ The average thermal energy cal/sec
≈ 4000 cal./sec