Q. Two persons are holding a rope of negligible weight tightly at its ends so that it is horizontal. A 15 kg weight is attached to rope at the mid-point which now no more remains horizontal. The minimum tension required to completely straighten the rope is
A) 15 kg
B) 15/2 kg
C) 5 kg
D) Infinitely large
Explanation
(d) Let $T$ be the tension in the string. Since the system is in equilibrium, therefore from figure
[image:5_image295.emf]
$2T\cos{\theta = mg}$
or $T = mg/2\ \ \cos\ \theta$
The string will be straight if $\theta = 90{^\circ}$
$\therefore\ T = mg/2\ \ cos\ 90{^\circ} = mg/2(0) = \infty$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.