The person is standing on a bathroom scale in an elevator. The bathroom scale is calibrated in newtons. This shows that the reading on the scale is the weight of the person. If the person's mass is M kg, the reading in the scale is F = M*a where a...

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The person is standing on a bathroom scale in an elevator. The bathroom scale is calibrated in newtons. This shows that the reading on the scale is the weight of the person. If the person's mass is M kg, the reading in the scale is F = M*a where a is the acceleration of the person and F is the resulting force applied on the scale.

When the elevator is descending at constant speed there is no force applied on the person and the net acceleration is zero. As a result the force exerted on the scale is M*0 = 0 N.

When the accelerator slows down there is a decrease in its velocity in the downward direction. Due to inertia the person continues to move downwards at the constant velocity that the elevator was moving at earlier. As the elevator has to come to a stop a force is exerted on the person in the upward direction which results in a counterforce applied by the person on the scale in the opposite direction. This is equal to M*a where a is the acceleration of the elevator. The scale shows a positive reading when this happens.