Q. A $10\ kg$ stone is suspended with a rope of breaking strength $30\ kg\ wt$. The minimum time in which the stone can be raised through a height $10\ m$ starting from rest is ( taking $g = 10\ N/kg)$
A) $0.5\ seconds$
B) $1.0\ seconds$
C) $\sqrt{\frac{2}{3}}\ seconds$
D) $2.0\ seconds$
Explanation
(b) The maximum tension $= 30 \times 10\ N = 300\ N$
$T - mg = ma$
$300 - 10 \times 10 = 10a$
$\Rightarrow a = 20\ m/s^{2}$ [Maximum value]
When the mass is raised, $u = 0,\ a = 20\ m/s^{2}$
$S = 10m,\ t = ?$
$10 = \frac{1}{2} \times 20.t^{2} \Rightarrow t = 1s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.