Question

A stone thrown upward with a speed $u$ from the top of the tower reaches the ground with a speed $3u$. The height of the tower is

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

Answer 1

The correct option is B $\frac{4u^2}{g}$

According to question, $v=3u$
By using third equation of motion
$v^2=u^2+2gh$
$\Rightarrow (3u{)}^2=(-u{)}^2+2gh$ (Take downward direction positive)
$\Rightarrow h=\frac{4u^2}{g}$