AP Physics C Mechanics Question of the Day

Practice AP Physics C Mechanics with the production-style question-of-the-day selection for this public URL.

Question 1

You are riding in an elevator that is accelerating upwards at , when you note that a block suspended vertically from a spring scale gives a reading of .

What does the spring scale read when the elevator is descending at constant speed?

Explanation: When the elevator accelerates upward, we know that an object would appear heavier. The normal force is the sum of all the forces added up, and in this case it is

. We know that the normal force has two components, a component from gravity, and a component from the acceleration of the elevator. Using this equation, we can determine the mass of the block, which doesn't change:

is acceleration due to gravity and

is the acceleration of the elevator. When substituting in the values, we get

Solving for

, we get

Since the elevator is descending at constant speed, no additional force is applied, therefore the force that the spring scale reads is only due to gravity, which is calculated by:

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AP Physics C Mechanics