Question

A projectile is projected at $10m{s}^{-1}$ by making at an angle ${60}^o$ to the horizontal. After some time its velocity makes an angle of ${30}^o$ to the horizontal. Its speed at this instant is.

• A. $\frac{10}{\sqrt{3}}$
• B. $10\sqrt{3}$
• C. $\frac{5}{\sqrt{3}}$
• D. $5\sqrt{3}$

Answer 1

The correct option is A $\frac{10}{\sqrt{3}}$

As the projectile has no acceleration in horizontal direction, thus its velocity component in horizontal direction remains constant.

Velocity component of projectile initially $V_x=10\cos {60}^o=10\times 0.5=5$ $m/s$

$\therefore$ Velocity component of projectile after some time $V_x^{\prime }=V_x=5$ $m/s$

Now angle made by speed with horizontal direction is ${30}^o$.

$\therefore$ Speed at this instant $V=\frac{V_x^{\prime }}{\cos {30}^o}=\frac{10}{\sqrt{3}}$ $m/s$