Kinematics Question 547
Question: A body of mass $ m $ hangs at one end of a string of length l, the other end of Which is fixed. It’s given a horizontal velocity so that the string would just reach where it makes an angle of $ 60^{o} $ with the vertical. The tension in the string at mean position it’s [ it’sM Dhanbad 1994]
Options:
A) $ 2mg $
B)$ mg $
C) $ 3mg $
D) $ \sqrt{3}mg $
Show Answer
Answer:
Correct Answer: A
Solution:
When body is released from the position p (inclined at angle q from vertical) then velocity at mean position $ v=\sqrt{2gl(1-\cos \theta )} $ \ Tension at the lowest point = $ mg+\frac{mv^{2}}{l} $
$ =mg+\frac{m}{l}[2gl(1-\cos 60)] $
$ =mg+mg=2mg $
