Question

A stone is thrown vertically upward with an initial velocity $u$ from the top of a tower, reaches the ground with a velocity $3u$. The height of the tower is

• A. $\frac{3u^2}{g}$
• B. $\frac{4u^2}{g}$
• C. $\frac{6u^2}{g}$
• D. $\frac{9u^2}{g}$

Answer 1

Answer: (B)

$\frac{4u^2}{g}$

Using the equations of the motion
$v^2=u^2+2gh$
$(3u{)}^2=u^2+2gh$
The height of the tower is, $h=\frac{4u^2}{g}$