Question

From the top of a building $80m$ high, a ball is thrown horizontally which hits the ground at a distance. The line joining the top of the building to the point where it hits the ground makes an angle of ${45}^o$ with the ground. Initial velocity of projection of the ball is $(g=10m/s^2)$

• A. $10m/s$
• B. $15m/s$
• C. $20m/s$
• D. $30m/s$

Answer 1

The correct option is C $20m/s$

Given Range $=80m$

In vertical direction :
$s=ut+\frac{1}{2}a{t}^2\Rightarrow -80=0+\frac{1}{2}\times (-10)t^2\Rightarrow t=4sec$

In horizontal direction :

$\upsilon =\frac{range}{t}=\frac{80}{4}m/s=20m/s$