Doubt from Mechanics


A constant horizontal force F = mg starts acting on a suspended pendulum bob of mass m, initially at rest. Let the maximum angular deflection of the string connecting point of suspension to the bob be {\theta}_1 and let {\theta}_2 the angular deflection when the tension of the string is maximum. If
N = {\theta}_1 + {\theta}_2, then find N.


N=pi/2 @Lavesh_2020


Answer is given 135 degree. theta 1 = 90 degree and theta 2 = 45 degree.


What you should do in this case is consider the fact that 2 constant forces are acting on the bob all the time i.e. mg - verically downwards and mg- horizontally so using vector addition we can clearly say net force is (2)^1/2 mg and 45° from vertical direction and now this situation is more or less equivalent to moving a normal pendulum 45°from vertical and in this case you could clearly tell theta1=90 and theta2=45.


How? Can you explain, please?


Take a normal pendulum now move it to the left by 45° and leave it . What would happen is the pendulum will oscillate between to two extremes which are 45°left and 45° right so deflection from initial position is simply 90° same is the case here it will initially be hanging vertically and finally it would be hanging horizontally..


Thanks a lot! :grinning:


Well currently none i used to be in Kota but i have already appeared in jee 2019. My username is actually botched and now i don't know how to rectify it..

1 Like