Of conservation of energy states that the energy can neither be created nor destroyed but can be transformed from one form to another.
let us now prove that the above law holds good in the case of a freely falling body.
Answers
Law of conservation of energy states that the energy can neither be created nor destroyed but can be transformed from one form to another.
Let us now prove that the above law holds good in the case of a freely falling body.
Let a body of mass 'm' placed at a height 'h' above the ground, start falling down from rest.
In this case we have to show that the total energy (potential energy + kinetic energy) of the body at A, B and C remains constant i.e., potential energy is completely transformed into kinetic energy.At A, Potential energy = mgh
Kinetic energy Kinetic energy = 0 [the velocity is zero as the object is initially at rest]
Total energy at A = Potential energy + Kinetic energy
Total energy at A = mgh …(1)
At B, Potential energy = mgh = mg(h - x) [Height from the ground is (h - x)]
Potential energy = mgh - mgx
Kinetic energy The body covers the distance x with a velocity v. We make use of the third equation of motion to obtain velocity of the body.
v2 - u2 = 2aS Here, u = 0, a = g and S = x
Kinetic energy = mgx
Total energy at B = Potential energy + Kinetic energy
Total energy at B = mgh …(2)
At C, Potential energy = m x g x 0 (h = 0)
Potential energy = 0 Kinetic energy
The distance covered by the body is h v2 - u2 = 2aS
Here, u = 0, a = g and S = h
Kinetic energy = mgh
Total energy at C = Potential energy + Kinetic energy = 0 + mgh
Total energy at C = mgh …(3)
It is clear from equations 1, 2 and 3 that the total energy of the body remains constant at every point. Thus, we conclude that law of conservation of energy holds good in the case of a freely falling body.
