Question

A metal ball of mass 2 kg is allowed to fall freely from rest from a height of 5 m above the ground. Taking g = 10 m s⁻², calculate:

1. the potential energy possessed by the ball when it is initially at rest.
2. the kinetic energy of the ball just before it hits the ground?

Answer 1

Mass of the ball m = 2 kg, g = 10 ms⁻², h = 5 m

(i) Potential Energy possessed by the ball = mgh

= 2 × 10 × 5

= 100 J

(ii) K.E of ball = potential Energy = 100 J

or v² = 2gh

v² = 2 × 10 × 5

= 100 J

∴ K.E = `1/2  mv^2`

= `1/2 xx 2 xx 100`

= 100 J