Question

Section B

a. A bicycle and a rider have a combined mass of 175 kg. How many calories of heat are generated in the brakes when the bicycle comes to a stop from a speed of 20 m/s? Take 4.18 J =1cal

            b.  If all the energy is trapped in a 1.5 kg aluminum bag without any heat       loss, how much will its temperature increase (DT) ? c = 0.220 cal/g°C.

Answer 1

Energy given by brake to stop the bicycle = (1/2) m v² = (1/2) 175 20 20 = 35000 J

Heat generated in brake = ( 35000 / 4.2 ) = 8333 cal

If 8333 calories of heat absorbed by 1.5 kg Aluminium , then rise in temperature

1.5 0.22 10³T = 8333

Hence rise in temperature T = 8333 /( 1.5 0.22 1000) = 25^o C