Q3 of 5 Page 158

A body of mass 5 kg is thrown vertically upwards with a speed of 10 metre per second, what is its kinetic energy when it is thrown? Find its potential energy when it reaches at the highest point also find the maximum height attained by the body.

Mass of body = 5kg = m

Initial speed = 10m/s = u


Kinetic energy =


= × 5kg × (10m/s)2


= × 5 × 100


= 250J


Final speed = 0m/s (at highest point)


Using 3rd equation of motion.


v2 = u2 – 2gs


(0)2 = (10m/s)2 – 2(9.8m/s2) s


0 = 100 – 19.6s


–100 = –19.6s


= s


5.102m = s = h


Potential energy = mgh


= 5 × 9.8 × 5.102


= 249.98J = 250J (approx.)


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