AP Physics 1 : Specific Forces

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #35 : Spring Force

A horizontal spring with constant  is on a frictionless surface with a block attached to one end. If the spring is compressed  and the instantaneous acceleration of the block is  after being released, what is the mass of the block?

Possible Answers:

Correct answer:

Explanation:

We can use Newton's second law to solve this problem:

Where the only force is from the spring, so we can say:

Rearranging for mass, we get:

Plugging in our values, we get:

Example Question #36 : Spring Force

A horizontal spring with constant  is on a surface with . A block of mass  is attached to the end of the spring. If the spring is compressed by  and released, what is the velocity of the block as it passes through the equilibrium of the spring?

Possible Answers:

Correct answer:

Explanation:

We can use the expression for conservation of energy to solve this problem:

There is no initial kinetic (starts at rest) or final potential (at equilibrium), so we can say:

Where work is done by friction. Inserting expressions for each of these, we get:

Multiplying both sides of the equation by 2 and rearranging for velocity, we get:

Plugging in values for each of these variables, we get:

Example Question #37 : Spring Force

A  spring is used to swing a  mass at . If the spring stretches by , determine the spring constant.

Possible Answers:

None of these

Correct answer:

Explanation:

The radius of the circle will be . This is the rest length plus the stretch of the spring.

Thus, the circumference will be

Since the angular velocity is

Thus, the linear velocity is

The force of the spring will be equal to the centripetal force.

Solving for the spring constant:

Plugging in values:

Example Question #31 : Spring Force

If a board depresses identical parallel springs by . Determine the spring constant.

Possible Answers:

Correct answer:

Explanation:

Using

Solving for

Converting to and plugging in values:

Example Question #31 : Spring Force

If a board depresses identical parallel springs by . Determine the compression if springs were used instead.

Possible Answers:

Correct answer:

Explanation:

Using

Solving for

Converting to and plugging in values:

Using

Solving for 

Converting to

Example Question #40 : Spring Force

A spring of rest length  is used to hold up a  rocket from the bottom as it is prepared for the launch pad. The spring compresses to . Determine the spring constant.

Possible Answers:

None of these

Correct answer:

Explanation:

The spring force is going to add to the gravitational force to equal zero.

Plugging in values:

Solving for

Example Question #41 : Spring Force

A spring of rest length  is used to hold up a  rocket from the bottom as it is prepared for the launch pad. The spring compresses to .

Later, the same spring is used to support a rocket of mass . Determine the compression.

Possible Answers:

None of these

Correct answer:

Explanation:

The spring force is going to add to the gravitational force to equal zero.

Plugging in values:

Solving for

Once again, using

Solving for

Example Question #42 : Spring Force

Two springs with unknown constants are attached in a linear fashion and hung from a ceiling. However, we do know that the constant of one spring is twice that of the other. A mass of  is attached to the bottom spring and the system drops . If you manually pull down the mass so the system stretches another , what is the maximum velocity of the block?

Possible Answers:

Correct answer:

Explanation:

Since we are never asked about anything pertaining to an individual spring, their individual constants and arrangement are irrelevant. We can simply use an equivalent resistance to solve this problem. Beginning with Hooke's Law:

Rearranging for the spring constant:

Plugging in our values, we get:

Now we have a value for our equivalent resistance. At this point, the system has set into a new equilibrium. This is very important to remember when performing further calculations.

Let's move on to the next relevant information: we manually pull down the mass an additional distance. We are ultimately looking for the maximum velocity of the spring. This occurs when the mass passes through our new equilibrium. Furthermore, we have enough information to calculate the potential energy of the spring when it is at it's maximum stretched length. Therefore, we can use the expression for conservation of energy:

Where the initial condition is when the spring is full stretched, and the final condition is when the mass passes through equilibrium. Therefore, we can eliminate initial kinetic and final potential energy to get:

Plugging in expressions for each of these, we get:

Rearranging for velocity, we get:

We have all of these values, so time to solve the problem:

Example Question #43 : Spring Force

A mass of  is attached to a spring with constant  that is hanging from a rope that is attached to a ceiling. If the mass has an amplitude of , what is the maximum tension in the rope? Ignore the mass of the rope and spring and assume simple harmonic motion.

Possible Answers:

Correct answer:

Explanation:

When in equilibrium, the tension in the rope is simply the weight of the mass:

The maximum tension will occur at the maximum extension of the spring, when 

We can then use Hooke's law to calculate the addition tension in the rope:

Adding the two together, we get:

Example Question #44 : Spring Force

A spring is attached to a rope that is hanging from the ceiling. A block of mass  is attached to the end of the spring which has a constant of . If the maximum tension felt in the rope is , what is the amplitude of the spring?

Ignore the mass of the rope and spring and assume simple harmonic motion.

Possible Answers:

Correct answer:

Explanation:

The tension in the rope is a result of the weight of the mass and the force of the spring:

Substituting expressions in for the two forces:

Rearranging for displacement, we get:

Plugging in our values, we get:

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