Question

A$2kg$ ball is dropped from a height of $10m$. Find its kinetic energy just before hitting the ground. [Take g $=10m{s}^{-2}$.]

Answer 1

Step 1: Given data

Mass of the ball, m =$2kg$

Height from which it is dropped, h = $10m$

Acceleration due to gravity, g = $10m{s}^{-2}$

Step 2: Finding the velocity while hitting the ground

Here the initial velocity is zero as it is dropped from a height. which implies u = $0$

We need to get the velocity (v) of the ball when it is about to hit the ground. As per the equation of motion,

$v^2-u^2=2as$ where, a = acceleration due to gravity and s =height.

$$\begin{gathered} v^2-0=2\times 10\times 10 \\ {v}^2=200 \end{gathered}$$

Step 3: Finding Kinetic energy

$$\begin{gathered} K.E=\frac{1}{2}m{v}^2 \\ K.E=\frac{1}{2}\times 2\times 200 \\ K.E=200J \end{gathered}$$

Therefore, the kinetic energy just before hitting the ground is $200J$.