Question

A stone is thrown upward with a speed ‘u’ from the top of a tower reaches the ground with velocity ‘3u’. The height of the tower is: (g = acceleration due to gravity)

Options

• `(3u^2)/g`

• `(4u^2)/g`

• `(6u^2)/g`

• `(9u^2)/g` 

Answer 1

`bb((4u^2)/g)`

Explanation:

The stone is thrown upwards,

∴ u = −u

Also, v = 3u

Using third kinemetical equation of motion,

v² = u² + 2as

As, the stone is in free fall,

a = g and s = h = height of the tower

∴ (3u)² = (−u)² + 2gh

∴ 9u² − u² = 2gh

∴ 8u² = 2gh

⇒ h = `(4 u^2)/g`