Question

A decoration, of mass M, is suspended by a string from the ceiling inside an elevator. The elevator is travelling upward with a constant speed. The tension in the string is
A) Equal to Mg
B) Less than Mg
C) Greater than Mg
D) Impossible to tell without knowing the speed.

Answer 1

We have given a case where a decoration of mass M is suspended by string from the ceiling inside an elevator which is moving with constant speed and we have to find the tension in the string. The tension in the string can be given by balancing the force experienced by the decoration.

Complete answer:
Let us first draw the a diagram for the given question for better understanding

Here v is the constant velocity of the elevator, T is tension in the string and Mg is the gravitational pull which will be experienced by the decoration due to gravity.
Now it is given that the elevator is moving with a constant velocity therefore there is no acceleration as acceleration is given as rate of change of velocity. So the only acceleration which the decoration is experiencing is due to the acceleration of the gravity.
Hence the only forces experienced by the decoration is the tension in the string and the downward gravitational pull. And from the diagram we can see that both are balancing each other therefore the tension in the string T is equal to the gravitational pull Mg.

So the correct option is A.

Note:
Note: In case the elevator has an acceleration then there will be an extra term due to the motion of the elevator and to find the tension we would have required the acceleration value in order to find T in terms of Mg. Also note that gravitational pull is due the mass of an object, a massless object will not experience the gravitational pull.