Question

A stone thrown upward with a speed u from the top of a tower reaches the ground with velocity3u the height of the tower is

Answer 1

Let the upward direction be positive

Initial velocity of the stone = u

Final velocity of the stone = - 3u  (negative, because the velocity is pointing in the opposite direction)

Acceleration due to gravity = - g = - 9.8 m/s^2

Let the height of the tower be h.

Using third equation of motion:

$v^2 = u^2 + 2ah$

$h = - \frac{(3u)^2-u^2}{2 \times 9.8}$

$h = - 0.41 u^2$ m

Hence, the height of the tower: $h = - 0.41 u^2$ m