Question

You are conducting an experiment inside a train car that may move along level rail tracks. A load is hung from the ceiling on a string. The load is not swinging, and the string is observed to make a constant angle of 45∘ with the horizontal. No other forces are acting on the load. Which of the following statements are correct? Check all that apply. 1 The train is an inertial frame of reference. 2 The train is not an inertial frame of reference. 3 The train may be instantaneously at rest. 4 The train may be moving at a constant speed in a straight line. 5 The train may be moving at a constant speed in a circle. 6 The train must be speeding up. 7 The train must be slowing down. 8 The train must be accelerating.

Answer 1

Here the weight is hung from the thread inside the ceiling of train

now the FBD of train is analysed

We can say

$Tcos\theta = mg$

$Tsin\theta = ma$

now by ratio of two equations we have

$a = gtan\theta$

this shows that train must be in accelerating condition due to which the thread is making an angle with the vertical

now we will have

2 The train is not an inertial frame of reference.

Since train is accelerating so it must be non inertial frame

5 The train may be moving at a constant speed in a circle.

Since its moving in circle so it is in accelerating condition

8 The train must be accelerating.