Question

A girl standing on a stationary lift (open from above) throws a ball upwards with initial speed $50 \,m \,s^{-1}$. The time taken by the ball to return to her hands is (Take $g= 10 \,m \,s^{-2}$)

• A. $5\,s$
• B. $10\,s$
• C. $15\,s$
• D. $20\,s$

Answer 1

Answer: (B)

$10\,s$

Answer 2

Using, $S=ut+\frac{1}{2} at^{2}$ Here $S = 0$, $u = 50\,m\,s^{-1}$, $a=-g=-10\,m\,s^{-2}$ $\therefore 0=50t+\frac{1}{2}\times\left(-10\right)t^{2}=50t-5t^{2}$ $\Rightarrow t=10\,s$