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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).

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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 

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