Question

From the top of a $19.6\text{m}$ high tower, a ball is thrown horizontally. If the line joining the point of projection to the point where it hits the ground, makes an angle of ${45}^{\circ }$ with the horizontal, then the initial velocity of the ball is

• A. $9.8\text{m/s}$
• B. $4.9\text{m/s}$
• C. $14.7\text{m/s}$
• D. $2.8\text{m/s}$

Answer 1

The correct option is A $9.8\text{m/s}$

Even though it seems to be projectile problem we can do it by equation of stratight line by breaking the components in horizontal and vertical.

Since, angle with the horizontal is ${45}^{\circ }$, therefore,
In horizontal direction,


In horizontal direction,
$19.6=u\times t$ (1)
In vertical direction,
$t=\sqrt{2h/g}=\sqrt{\frac{2\times 19.6}{9.8}}=2\text{sec}$
By putting value of $t$ in equation (1) we get,
​​​​​​ $u=9.8\text{m/s}$
Hence, the correct answer is option (a).