A body is projected up vertically with a velocity of 60 m/s. What percentage of its initial kinetic energy is converted into potential energy after 3 seconds? (Take g = 10 m/s^2)

(a) 25 %

(b) 50%

(c) 75%

(d) 100%

I had been asked this question by my school teacher while I was bunking the class.

My query is from Kinetic Energy in section Work, Energy and Power of Physics – Class 11

Select the correct answer from above options

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Correct answer is (c) 75%

Best explanation: Initial KE = (1/2) x M x (60 x 60)

= 1800 x M

From Newton’s laws;

s = ut + (1/2)gt^2

= (60 x 3) – (10 x 3 x 3)/2

= 180 – 45

= 135 m

Potential energy at 135m (PE) = M x g x s

= 1350 x M

So KE at 135m = Initial KE – PE

= 1800M – 1350M

= 450M J; This is 25% of the initial kinetic energy. Hence, 75% is converted into potential energy.