Question

An elevator is goning vertically up with a constant acceleration of $2m/s^2$. At the instant when its velocity is $4m/s$ a ball is projected from the floor of the elevator with a speed of $4m/s$ relative to the floor with an angular elevation of ${60}^o$. The time taken by the ball to return the floor is $(g=10m/s^2)$.

• A. $\frac{1}{3}\sec$
• B. $1\sec$
• C. $\frac{2}{\sqrt{3}}\sec$
• D. $\sqrt{3}\sec$

Answer 1

The correct option is A $\frac{1}{3}\sec$

Components of velocity of ball relative to lift are$:$

$u_x=4\cos {30}^0=2\sqrt{3}m/s$

$u_y=4\sin {30}^0=2m/s$

$T=\frac{2u_y}{12}=\frac{u_y}{6}=\frac{2}{6}=\frac{1}{3}s$

Hence,

option $\left(A\right)$ is correct answer.