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Question

What will happen to a person's weight when he is in a moving elevator?

This question was previously asked in
RRB NTPC 2015 CBT 1 Question Paper (29-Mar-2016) (Shift 1)
The correct answer is
Weight will not change

Elevator Weight Physics Explained

A person's weight is determined by the normal force ($N$) exerted by the supporting surface (the elevator floor). This apparent weight equals the true weight (gravitational force, $mg$) only when the net force is zero.

Analyzing Forces in Moving Elevator

We apply Newton's Second Law ($\Sigma F = ma$) to the person inside the elevator. The forces involved are:

  • The downward gravitational force ($mg$).
  • The upward normal force from the floor ($N$).

The net force equation is: $N - mg = ma$ where '$a$' is the acceleration of the elevator.

Scenario: Constant Velocity Motion

The question implies a scenario where the weight does not change. This occurs when the elevator moves at a constant velocity (or is at rest). In this specific case, the acceleration ($a$) is zero.

Substituting $a = 0$ into the equation:

$N - mg = m(0)$ $N - mg = 0$ $N = mg$

When $N = mg$, the apparent weight is equal to the true gravitational force. Thus, the person's weight does not change.

Conclusion: In a moving elevator at constant velocity, the apparent weight remains the same.

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