Question

An open lift is moving upwards with velocity 10 m/s. It has an upward acceleration of 2 m/s${}^2$. A ball is projected upwards with velocity 20 m/s relative to ground. Find the time when ball again meets the lift.

• A. $\frac{4}{3}s$
• B. $\frac{5}{3}s$
• C. $\frac{5}{4}s$
• D. $\text{None}$

Answer 1

The correct option is B $\frac{5}{3}s$

At the time when ball again meets the lift, $s_L=s_B$
$\therefore 10t+\frac{1}{2}\times 2\times t^2=20t-\frac{1}{2}\times 10t^2$
Solving this equation, we get
$\therefore$ Ball will again meet the lift after $\frac{5}{3}s.$