AP Physics 1 : Circular, Rotational, and Harmonic Motion

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #181 : Circular, Rotational, And Harmonic Motion

If a period of a pendulum is , what is its length?

Possible Answers:

None of these

Correct answer:

Explanation:

Equation for period of a pendulum:

Solve.

Example Question #4 : Period And Frequency Of Harmonic Motion

In the lab, a student has created an oscillator by hanging a weight from a spring. The student releases the oscillator from rest and uses a sensor and computer to find the equation of motion for the oscillator: 

The student then replaces the weight with a weight whose mass,  is twice as large as that of the original weight.The student again releases the weight from rest from the same displacement from equilibrium. What would the new equation of motion be for the oscillator?

Possible Answers:

Correct answer:

Explanation:

The equation of motion for an oscillator is:

In words, the position as a function of time equals the amplitude times the cosine of the sum of the frequency (in radians per second) times time plus phase. Changing the mass of the weight only changes the frequency, but it depends upon the square root of the mass. Since increasing the mass increases the period, it decreases the frequency by the factor of .

Example Question #2 : Period And Frequency Of Harmonic Motion

The Fourier Transform is an extensively used mathematical analysis technique. In some applications, it reconstructs a function  into an infinite series of sine waves. 

Given that the Fourier Transform is given by the series: 

 

Where  is an arbitrary length and  is an integer, what is the wavelength of the sinusoid when 

Possible Answers:

Correct answer:

Explanation:

First, we want to ignore the summation sign and the  since those terms do not affect the wavelength at . All we need to look at is the sine term. 

For , we get the sinusoid:

 

Remember that wavelength  is given by 

Example Question #182 : Circular, Rotational, And Harmonic Motion

Determine the period of a sine wave that has a frequency of .

Possible Answers:

Correct answer:

Explanation:

Period is given by:  where  is frequency. Therefore,

Example Question #181 : Circular, Rotational, And Harmonic Motion

A horizontal spring with a constant  is on a frictionless surface. If the mass is doubled, by what factor is the frequency of the spring changed? Assume simple harmonic motion.

Possible Answers:

Correct answer:

Explanation:

The expression for the frequency of a spring:

Therefore, we can say:

Where:

Substituting this into our expression, we get:

Taking the inverse of both sides:

Rearranging for final frequency:

From the problem statement, we know that:

substituting this into the expression, we get:

Therefore, the frequency was changed by a factor of 

Example Question #182 : Circular, Rotational, And Harmonic Motion

A simple pendulum has a block of mass  attached to one end and is rotating in simple harmonic motion. If the frequency of the pendulum is , what is the length of the pendulum?

Possible Answers:

Correct answer:

Explanation:

We only need one expression to solve this problem:

Now we just need to rearrange for the length of the pendulum:

We have values for each of these variables, so time to plug and chug:

Example Question #11 : Period And Frequency Of Harmonic Motion

If the length of a simple pendulum is halved and the pendulum is moved to the moon where , by what factor does the period of the pendulum change when this is done?

Possible Answers:

Correct answer:

Explanation:

Since we are told that this is a simple pendulum, we can use the follow expression for period:

Now let's divide scenario 2 by scenario 1:

From the problem statement, we know that:

So let's plug that in:

Then plugging in our values for g:

Example Question #183 : Circular, Rotational, And Harmonic Motion

As on object passes through its equilibrium position during simple harmonic motion, which statements are true regarding its potential (U) and kinetic (K) energies?

Possible Answers:

min U, max K

min U, min K

max U, min K

None of these

max U, max K

Correct answer:

min U, max K

Explanation:

An object has the maximum potential energy the furthest from its equilibrium point (at the turnaround point). So it at the equilibrium position it would have the minimum potential energy. If it is undergoing simple harmonic motion, it would have the maximum kinetic energy as it passes through the equilibrium position because it is returning from the stretched position (spring example) where it gathered energy. The same is true for other objects undergoing this motion.

Example Question #184 : Circular, Rotational, And Harmonic Motion

Find the mass of the bob of a simple pendulum if the period of the pendulum is  seconds, and the length of the pendulum is .

Possible Answers:

Impossible to determine

Correct answer:

Impossible to determine

Explanation:

It's impossible because the period of a simple pendulum doesn't depend on the mass of the bob. Because of this, we have no way to determine the mass from the period.

Example Question #185 : Circular, Rotational, And Harmonic Motion

The position of a  mass in an oscillating spring-mass system is given by the following equation:

, where  is measured in , and  is measured in .

What is the frequency of the system?

Possible Answers:

Correct answer:

Explanation:

In these types of problems, it is always advantageous to recognize the format of the equation. In trigonometric functions, the period is always given by , when the function is written as . Since frequency is the reciprocal of the period, we will need to flip the fraction.

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