Question

An object is thrown vertically upwards with a speed ‘u’. What is its velocity just before reaching the ground?

Answer 1

1. When an object is thrown upward under the influence of gravity, it reaches its highest point by gradually decreasing its velocity.
2. After reaching the highest point, it reverses its direction and freely falls back to the ground due to the gravitational force of the earth.
3. The initial velocity of a freely falling body is 'zero'.
4. The acceleration of the body is ‘g’.
5. Let ‘h’ be the distance covered by the object during free fall.
6. Now from the equation $v^2-u^2=2as$, we can calculate its final velocity just before reaching the ground.

$$\begin{gathered} v^2-{\left(0\right)}^2=2gh \\ \Rightarrow v^2=2gh \\ \Rightarrow v=\sqrt{2gh} \end{gathered}$$

Hence, the velocity of the object just before reaching the ground is equal to $\sqrt{2gh}$