Chapter 11 WORK AND ENERGY

Two girls, each of weight 400 N climb up a rope through a height of 8 m. We name one of the girls A and the other B. Girl A takes 20 s while B takes 50 s to accomplish this task. What is the power expended by each girl?

Solution:(i) Power expended by girl A:Weight of the girl, mg = 400 NDisplacement (height), h = 8 m Time taken, t = 20 sPower, P = Work done / time taken Power = mgh / t P = 400 N × 8 m / 20 s= 160 W. (ii) Power expended by girl B:Weight of …

Two girls, each of weight 400 N climb up a rope through a height of 8 m. We name one of the girls A and the other B. Girl A takes 20 s while B takes 50 s to accomplish this task. What is the power expended by each girl? Read More »

A boy of mass 50 kg runs up a staircase of 45 steps in 9 s. If the height of each step is 15 cm, find his power. Take g = 10 m s–2 .

Solution:Weight of the boy,w = mg = 50 kg × 10 m s–2 = 500 NHeight of the staircase,h = 45 × 15/100 m = 6.75 mTime taken to climb, t = 9 s, power, P = Work done/time taken mgh / t Power (P) = (500 N × 6.75 m ) / 9s= 375 …

A boy of mass 50 kg runs up a staircase of 45 steps in 9 s. If the height of each step is 15 cm, find his power. Take g = 10 m s–2 . Read More »