Question

How high must a body be lifted to gain an amount of P.E. equal to the K.E. it has when moving at speed 20 ms^–1. (The value of acceleration due to gravity at a place is 9.8 ms^–2).

Answer 1

Given,

KE = PE = 1/2× m×v×v = m×g×h = 1/2× 20×20×m = m×10×h (assume g=10) 

= 1/2× 20×20 = 10×h = 10×20 = 10h = 200 = 10h 

= 200/10 = H = H = 20 

So the height is 20m