Question

90. A train having 60 wagons each weighing 25 tonnes is moving with a speed of \( 72 km / h \). If the frictional force is \( 10 N \) per tonne, the power developed is a) \( 3 \times 10^{5} W \) b) \( 3 \times 10^{6} W \) c) \( 3 \times 10^{7} W \) d) \( 3 \times 10^{4} W \)

Answer 1

Correct option is a) 3 x 10⁵ W

Given that,

mass of each wagons, m = 25 tonnes 

Number of wagons = 60 

Speed of train, V = 72 km/hr

= 72 x \(\frac {5}{18}\,m/s\)

= 20 m/s

Frictional force Per tonne, f = 10 N

Total Mass of train = 60 x 25 tonnes 

= 1500 tonnes

Total frictional force on train,

F = 1500 x 10 N 

= 15000 

Power = F.V

Power developed = FV 

= 15000 N. x 20 m/s 

= 300000 N. m/s 

= 3 x 10⁵ W