Question

Question 4

Part A

Predict how the upward force exerted on the feet by the scale will compare to the weight of the man if the elevator is moving upward at a constant speed.

The upward force on the feet will be equal to the man’s weight.

The upward force on the feet will exceed the man’s weight.

The upward force on the feet will be less than the man’s weight.

Part B

Predict how the upward force exerted on the feet by the scale will compare to the man’s weight if the elevator is moving downward at a constant speed.

The upward force on the feet will be equal to the man’s weight.

The upward force on the feet will exceed the man’s weight.

The upward force on the feet will be less than the man’s weight.

Part C

Predict how the upward force exerted on the feet by the scale will compare to the man’s weight if the elevator is accelerating upward.

The upward force on the feet will be equal to the man’s weight.

The upward force on the feet will be less than the man’s weight.

Part D

Predict how the upward force exerted on the feet by the scale will compare to the man’s weight if the elevator is accelerating downward.

The upward force on the feet will be equal to the man’s weight.

The upward force on the feet will exceed the man’s weight.

The upward force on the feet will be less than the man’s weight.

Answer 1

Sol:

Part A - The upward force on the feet will be equals to the man's weight, since no extra force act on the body and only force is mg where m is mass and g is acceleration due to gravity.

Part B - The upward force on the feet will be equals to the man's weight, at constant velocity weight is unchanged and is mg.

Part C - The upward force will exceed the man's weight , while accelerating upward net force will be F+F' where F is due to gravity and F' is the reaction force of the force due to gravity hence weight will exceed slightly.

Part D - The upward force on the feet will be less than the man's weight, the net force will be F-F' while F and F' are same as in part c , hence the man will feel lighter.

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