Question

prove that energy remain constant in case of free falling body

Answer 1

m = mass of body

g = Acceleration due to gravity

Suppose a body is at point A initially. Then it falls freely, during the motion mechanical energy of the body is conserve.

At point A,

AC = height of object from ground

       = h

Initial speed u = 0

So, P.E. = mgh



TE = P.E + K.E = mgh + 0

(TE)A = mgh ... (i)

At point B,

PE = mg (BC)

= mg (h – x) = mgh – mgx

Use kinematics equation



(TE)B = P.E. + K.E = mgh – mgx + mgx

= mgh ...(ii)

At point C,

P.E. = 0



Use kinematics equation



⇒ v 2 = 2gh

So, 

(T.E.)C = K.E + P.E. = mgh +0 = mgh ...(iii)

(TE)A =(TE)B=(TE)C

Hence, the total energy of the body is conserve during free fall.