Question

A girl throws a ball vertically upwards with an initial speed of $15m/s$. The ball was released when it was at $2.0m$ above the ground. The girl catches it at the same point as the point of projection. What is the maximum height reached by the ball?

• A. $11.5m$
• B. $13.5m$
• C. $15.5m$
• D. $17.5m$

Answer 1

The correct option is B $13.5m$

The ball will continue to move upwards as long as it has velocity. At maximum height $v=0$. We choose point of projection as origin, and upward direction to be positive.

From the equation, $v_y^2=u_y^2+2a_{y}y$
$v_y^2=u_y^2-2gy$
At maximum height,
$y_{max}=\frac{u_y^2}{2g}$
$=\frac{{15}^2}{2\times 9.8}=11.5$
$y=y_{max}+2=11.5+2=13.5\text{m}$