AP Physics C: Mechanics : Using Pendulum Equations

Study concepts, example questions & explanations for AP Physics C: Mechanics

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Example Questions

Example Question #1 : Using Pendulum Equations

A simple pendulum of length  swings at a radius  from a fixed point on the ceiling. As it moves, the pendulum creates an angle  with the line that extends vertically downwards from the fixed point. At what angle does the mass attached to the pendulum have the highest kinetic energy? 

Possible Answers:


Correct answer:


The correct answer is . Since the pendulum is at the bottom of its motion at this point, it has the lowest amount of energy given to gravitational potential and thus, the highest kinetic energy. 

Example Question #2 : Using Pendulum Equations

If a simple pendulum is constructed using a  rope of negligible weight and a large steel ball weighing . What is the period of the pendulum?

Possible Answers:

Not enough information


Correct answer:


Use the equation for the period of a simple pendulum:


Here,  is the period in seconds,  is the length of the pendulum in meters, and  is the acceleration due to gravity in .

We can plug in the given quantities for length and acceleration to solve for the period.

Note that the mass of the rope as negligible. We also need not incorporate the extraneous information regarding the weight of the steel ball attached to the pendulum. This does not influence the period of this simple pendulum.

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