Question

A ball is thrown vertically upwards from the top of a tower with a velocity of ${10ms}^{-1}$. The ball reaches the ground with the velocity ${30ms}^{-1}$. What is the height of the tower? $(Takeg={10ms}^{-2})$

• A. 40 m
• B. 20 m
• C. 60 m
• D. 80 m

Answer 1

The correct option is A 40 m

Taking downward direction to be positive.

Initial velocity $u=-10m/s$

Final velocity $v=30m/s$

Let the height of the tower be $H$.

Acceleration $a=g=10m/s^2$

Using $v^2-u^2=2aH$

$\therefore$ ${30}^2-(-10{)}^2=2\times 10\times H$

$⟹H=40m$