Question

Imagine a small RC – helicopter hovering in a resting train. The doors close and the train starts to move. Will the helicopter:
A. stay mid air
B. move with train
C. smack against the wall

Answer 1

Hint: Here we need to use the concept of motion in a straight line. We need to observe or imagine the movement of a hovering helicopter inside the train which was initially at rest and then starts to move. We need to know about the concept of relative motion of an object with respect to others. Here we will look at the relative motion of helicopters with respect to trains.

Complete answer:
Let us imagine the helicopter in the train exactly as mentioned in the question: the helicopter is hovering, hence its movement is affected only by the air that is surrounding it. Initially when the train is at rest the air around the helicopter wings also remains the same. Hence there is no motion. But the condition is that the train starts to move. Under this condition the doors are also closed. Before going to this part let's imagine about us.

Imagine that you are sitting in the bus when it is initially at rest. What happens to you when the bus starts to move? You see that you will fall backwards when the bus moves forward. Do you know why this happens? This happens because the lower part of the body of the person is in contact with the bottom of the bus. Hence when the bus starts to move the lower part of the body also moves along with it whereas the upper part of the body remains at rest because of inertia.

Now let's get back to the question. Here no part of the helicopter is in contact with the base of the train as it is hovering. Hence even when the train moves there would be no relative motion between the helicopter and train. The next factor that might affect the helicopter would be air surrounding it. To take this into consideration it's given that the windows are closed. It means even air difference is not there.Hence by taking into consideration all the given points above the conclusion would be that the helicopter stays in the mid air.

Hence the correct option is A.

Additional information:
Relative motion: It is defined as the motion of an object with respect to some other object which might be moving stationary or accelerated.
Inertia: It is a property by which an object continues to be in a state of rest or uniform motion in a straight line unless an external factor affects it or acts on it.

Note: We might get mistaken by the fact that the helicopter might move back and hit to the wall because that’s what happens when we sit in a train , but that is not applicable here because the helicopter is no way in contact with train from the initial state ( when train was at rest).