Q. The string of a pendulum of length $l$ is displaced through $90{^\circ}$ from the vertical and released. Then the minimum strength of the string in order to withstand the tension as the pendulum passes through the mean position is
A) $mg$
B) $6\ mg$
C) $3\ mg$
D) 5$\ mg$
Explanation
(c) Velocity at the lowest point, $v = \sqrt{2gl}$
At the lowest point, the tension in the string
$T = mg + \frac{mv^{2}}{l} = mg + \frac{m}{l}(2gl) = 3mg$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.