AP Physics 1 : Spring Force

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #21 : Spring Force

A narrow spring is placed inside a wider spring of the same length. The spring constant of the wider spring is twice that of the narrow spring. The two-spring-system is used to hold up a box of mass . They compress by .

Determine the spring constant of the wider spring.

Possible Answers:

Correct answer:

Explanation:

Use Hooke's law:

and

Wide spring:

Narrow spring:

From given information:

Substitute:

Summation of forces:

Where is pointing down and thus a negative value. Convert  to and plug in values:

Solve for :

Plug back into the following formula and solve for the spring constant of the wider spring.

Example Question #22 : Spring Force

A narrow spring is placed inside a wider spring of the same length. The spring constant of the wider spring is twice that of the narrow spring. The two-spring-system is used to hold up a box of mass . They compress by .

Determine the spring constant of the narrower spring.

Possible Answers:

Correct answer:

Explanation:

Use Hooke's law:

and

Wide spring:

Narrow spring:

From given information:

Substitute:

Summation of forces:

Where is pointing down and thus a negative value. Convert  to and plug in values:

Solve for :

Example Question #23 : Spring Force

A certain spring is held stretched  from its equilibrium position by a force of . The spring is then stretched further to a position  from its equilibrium.

How much work was done in stretching the spring from  to ?

Possible Answers:

Correct answer:

Explanation:

The spring is held outside of equilibrium at rest by a certain force. That means that this force is equal in magnitude to the restoring force of the spring. By Hooke's law, the magnitude of the restoring force is given by 

Where  is the spring constant, and  is the displacement of the spring. If  is the force that keeps the spring stretched, then . Solving for  gives us 

Now we need to find the work required to stretch the spring further from  to . Well, we know that the work done is equal to the negative of the change in potential energy of the spring by the work-energy theorem. The change in energy is given by: 

Therefore the work done is just the negative of the above, or 

Example Question #21 : Spring Force

One spring is placed inside of another. They both have the same spring constant. Together, they are used to suspend a mass of from the ceiling. They each stretch . Determine the spring constant of each.

Possible Answers:

Correct answer:

Explanation:

Example Question #21 : Spring Force

One spring is placed inside of another. They both have the same spring constant. Together, they are used to suspend a mass of from the ceiling. They each stretch . Determine the total stretch if they instead supported the same mass while attached end to end.

Possible Answers:

Correct answer:

Explanation:

Use Hooke's law and plug in known values:

Each spring will stretch the same amount,

Example Question #26 : Spring Force

Two springs are attached end to end. They have the same spring constant. They stretch a total of when they are used to suspend a mass of from the ceiling. Calculate the spring constant of each individual spring.

Possible Answers:

Correct answer:

Explanation:

Use Hooke's law:

Each spring stretched the same amount, , for a total stretch of .

Plug in values:

Solve for :

Example Question #21 : Spring Force

Two springs are attached end to end. They have the same spring constant. They stretch a total of when they are used to suspend a mass of from the ceiling. Determine the total stretch if instead the springs were used to hold up the same mass in parallel.

Possible Answers:

Correct answer:

Explanation:

Use Hooke's law:

Each spring stretched the same amount, , for a total stretch of .

Plug in values:

Solve for :

Now find the stretch distance if the springs were used in parallel.

Plug in values:

Solve for :

Example Question #28 : Spring Force

A  mass is hanging from a spring in equilibrium.  If the spring is stretched by a distance of , calculate the spring-constant .

Possible Answers:

Correct answer:

Explanation:

Since the mass in in equilibrium, this tells us the net force .  Writing the forces acting on the mass,

.  This allows us to solve for the spring constant.

Example Question #29 : Spring Force

If a spring of constant  has a potential energy , calculate the compression  of the spring.

Possible Answers:

Correct answer:

Explanation:

From the definition of the spring potential, 

Plugging in the given values lets us arrive at a calculated compression,

Example Question #30 : Spring Force

A vertical spring has a constant  and an equilibrium height of . If you want to use the spring to launch an object of mass  to a height of , how far must the spring be depressed from equilibrium?

Possible Answers:

Correct answer:

Explanation:

We can calculate the energy needed to be stored in the spring from the change in potential energy that the object experiences:

Where our change in height is going to be the distance between its high point and the point when the spring is compressed. Furthermore, this change in potential energy will be equal to the energy stored in the spring:

 was used since we're dealing with vertical distances. Setting these equal to each other:

We can also develop an expression for the change in height:

Substituting this back into our expression:

Distributing and rearranging:

Plugging in our values, we get:

Using the quadratic formula, we get:

 or 

Where a positive distance represents compression of the spring, and a negative distance represents extension of the spring. Therefore, the positive distance is our answer.

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