Q. A stone thrown vertically upwards attains a maximum height of 45m. In what time the velocity of stone become equal to one-half the velocity of throw? (Given $g = 10ms^{- 2}$)
A) 2 s
B) 1.5 s
C) 1 s
D) 0.5 s
Explanation
(b) Let us solve the problem in terms initial velocity, relative acceleration and relative displacement of the coin with respect to floor of the lift.
$u = 10 - 10 = ms^{- 1},a = 9.8ms^{- 2},S = 4.9m,t = ?$
4.9 =0$\times t + \frac{1}{2} \times 9.8 \times t^{2}$ or $4.9t^{2} = 4.9$ or $t = 1$s
$15 = 30 - 10t$ or $10t = 15$ or $t = 1.5$s
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.