Question

A pendulum bob of mass 50 g is suspended on a string from the ceiling of an elevator which is moving downwards with an acceleration 1.5 metre per second square . Draw the free body diagram using the non inertial frame of,reference and determine the tension in the string . ( Take g = 10 ms-2)

Answer 1

m = 50 gm,    g = 10 m/s^2

acceleration downwards of the elevator ,  a = 1.5 m/s^2  

Frame of reference:

     non-inertial frame.  A coordinate access attached to the elevator.

 

  In the non-inertial frame, we add a pseudo force on each object having a mass in the direction opposite to the movement of the frame.  So add a pseudo force on pendulum upwards = m a = 0.050 * 1.5 = 0.075 N

There is the weight of pendulum m g = 0.50  N  acting downwards.

There is tension T in the string acting upwards on the pendulum.

As the pendulum is at rest in the non-inertial frame:

     T + 0.075 N = 0.50 N

     T = 0.425 N