Question

A ball of mass 200 g falls from a height of 5 metres. What is its kinetic energy when it just reaches the ground? (g = 9.8 m/s²)

Answer 1

Mass of the ball, (m) = 0.2 kg
Height from which the ball is dropped, (h) = 5 m
Initial velocity of the ball, (u) = 0 m/s
Acceleration due to gravity, (g) = 9.8 m/s²
Let the final velocity of the ball when it just reaches the ground be (v)
We will use the third equation of motion to find the velocity of the ball when it just reaches the ground,
v² = u² + 2as
So,
v² = 0 + 2(9.8)(5)
⇒ v² = 98
Now we can find the kinetic energy as,
$K.E=\frac{1}{2}m{v}^2$
Therefore,
K.E = (1/2)(0.2)(98)
⇒ K.E = 9.8 J
So, the kinetic energy of the moving object is 9.8 J.