Q. A 24 kg block resting on a floor has a rope tied to its top. The maximum tension, the rope can withstand without breaking is 310 N. The minimum time in which the block can be lifted a vertical distance of 4.6 m by pulling on the rope is
A) 1.2 s
B) 1.3 s
C) 1.7 s
D) 2.3 s
Explanation
(c) Effective upward force = 310 $–mg$
$= 310 - 24 \times 9.8 = 74.8$ N
Upward acceleration
$\therefore a = 74.8/24 = 3.12\ ms^{- 2}$
As $s = ut + \frac{1}{2}at^{2}$
4.6 $= 0 + \frac{1}{2} \times 3.12 \times t^{2}$
or $t^{2} = \frac{4.6}{1.56} = 2.95$
or $t = \sqrt{2.95} = 1.7$s
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.