Question

A stone thrown upward with a speed $u$ from the top of a tower reaches the ground with a speed $4u$. The height of the tower is

• A. $\frac{15u^2}{2g}$
• B. $\frac{7u^2}{2g}$
• C. $\frac{16u^2}{g}$
• D. $\text{Zero}$

Answer 1

The correct option is A $\frac{15u^2}{2g}$

Using the 3rd equation of Motion,
$v^2=u^2+2as$
And putting the given values
$(4u{)}^2=u^2+2gh$
$\frac{16u^2-u^2}{2g}=h\Rightarrow h=\frac{15u^2}{2g}$