Question

3.a) A metal ball of mass 60 g falls on a concrete floor from a vertical height of 2.8m and rebounds to a height of 1.3 m. Find the change in P.E.

Answer 1

Given :-

Mass of ball = m = 60 g = 0.06 Kg

Acceleration due to gravity = g = 10 ms-²

Height coming down = H = 2.8 m

Height rebounds = h = 1.3 m

While coming down Potential Energy,

P.E. = mgh

P.E. = 0.06(10)(2.8)

P.E. = 1.68 J

Again while rebounds,

Here, Acceleration will act in opposite direction of motion,

g = -10 ms-²

P.E.' = mgh

P.E.' = 0.06(-10)(1.3)

P.E.' = -0.78 J

Negative Sign indicates that Potential Energy is acting in opposite direction.

∆P.E. = P.E. - P.E.'

∆P.E. = 1.68 - (-0.78)

∆P.E. = 2.46 J