Question

A boy playing on the roof of a $10m$ high building throws a ball with a speed of $10m/s$ at an angle of ${30}^o$ with horizontal. How far from the throwing point will the ball be at the height of $10m$ from the ground ? $(g=10m/s^2)$

• A. $5.20m$
• B. $4.33m$
• C. $2.60m$
• D. $8.66m$

Answer 1

The correct option is D $8.66m$

We want distance of the point P where height of ball from ground is $10m$. This is the value of range as roof height is same as of point P(at height $10m$)

Range $=\frac{v^2\sin 2\theta }{g}=\frac{{10}^2\sin {60}^0}{g}=10\sin {60}^0$$=\frac{10\sqrt{3}}{2}=8.66m$