Suppose your weight is 120 lb. You are riding in an elevator in the Sears tower.

Question

Suppose your weight is 120 lb. You are riding in an elevator in the Sears tower. while standing on

bathrooms scale and watching readings.

Imagine that the elevator keeps descending at a constant speed of 8 m/s.

1. What would be the reading on the scale (known as your “apparent weight”?)

Imagine that the elevator descends faster and faster, gaining speed at a constant rate (i.e. the acceleration of the motion is constant.)

2. What would happen to the reading on the bathroom scale?

Imagine that the elevator cable snapped and the elevator car is falling down the elevator shaft. You stay cool and watch the reading on the bathroom scale.

3.What reading do you see?

4.What’s your weight then?

5.Explain the difference between the “apparent weight” and the weight.

Planet X has the same mass as the Earth, but 1/2 the radius. (Planet X is more

dense than Earth).

1.What would be your mass on a surface of Planet X?

2.What would be your weight on a surface of Planet X?

3. Suppose you stand on a top of a very tall ladder ,and so your distance from the center of the Planet X is now equal to the Earth radius. What would be your weight there?

Explanation / Answer

Imagine that the elevator keeps descending at a constant speed of 8 m/s.

(1) In this case acceleration is zero so apparent weight would be equal to the actual weight

W = 120 lb

Imagine that the elevator descends faster and faster, gaining speed at a constant rate (i.e. the acceleration of the motion is constant.)

(2) In this case net accelration is in downward direction and apparent weight is the measure of the tension in the cable

here mg is greater as the acceleration is in downward direction so apparent weight would be less

Imagine that the elevator cable snapped and the elevator car is falling down the elevator shaft. You stay cool and watch the reading on the bathroom scale.

(3) In this case tension in the cable would be zero and both scale and the person would fall with the same acceleration and hence scale reading would be Zero

(4) Weight would remain same but we can not measure it in this case so apparent weight would be zero

but weight is still 120 lb

(5) Weight is the force by the earth on the person

and apparent weight is the force which we feel by the earth (we call it normal force)

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