Question

When a pendulum is displaced through 90°, the length l and mass m of the pendulum, the strength of the string that can withstand minimum tension is: ?

Answer 1

Answer;

There is centrifugal force acting over it so,  mv^2 / r.

When the pendulumn was released its potential energy became kinetic energy. Hence, we can say that,

mgl = 1/2mv^2

gl = 1/2 v ^ 2

v   =  √2gl

Let tension be x.

x ≥ mg + mv^2 / r  

x   ≥ mg +  m * 2gl / l     ( r = l )

x ≥ mg + 2mg

x  ≥  3mg

Hence, minimum tension is 3mg