Question

(a) Two bodies of equal masses move with uniform velocities v and 3v respectively. Find the ratio of their kinetic energies. 

(b) An electric heater is rated 1500 W. How much energy does it use in 10 h? 

Express your answer in              (i) kWh                  (ii) Joules

Answer 1

(a) Kinetic energy ∝ v² . 

Therefore, for energies KE₁ and KE₂,

(b) Given, 

Power, P = 1500 W = 1.5 kW, Time, t = 10 h 

(i) Energy = Power × time = 1.5 × 10 = 15 kWh 

(ii) 15 kWh = 15 × 3.6 × 10⁶ J                [ 1 kWh = 3.6 × 10⁶ J ]