Question

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

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

Answer 1

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

Initial velocity$=+u$
Final velocity $=-3u$
acc$=-g$
$h=$?
$v^2=u^2+2gh$
$9u^2=v^2-2gh$
$8u^2=-2gh$
$h=-\frac{4u^2}{g}$ (-ve means downward displacement)