Question
Calculate the potential energy of a body of mass 50 kg raised to a height of 4 m above the ground. If the body falls down under gravity freely, then what will be its velocity when it just touches the ground? (Given g = 9.8 m/s2) [Ans. 1960 J, 8.9 m/s (approx)]
Answer
Mass (m) = 50 kg
Height (h) = 4 m and g = 9.8 m/s2
(i) Calculation of Potential Energy
PE = m×g×h
= 50×9.8×4
= 1960 J
(ii) Calculation of velocity
Kinetic Energy = Potential Energy
or, {1\over2}×m×v^2 = 1960
or, {1\over2}×50×v^2 = 1960
or, v2 = 1960×2\over 50
or, v = √78.4 = 8.85 m/s
