AP Physics 1 : Forces

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #11 : Spring Force

A helicopter uses a rest length spring to pull up a submarine. The upward acceleration is . The spring stretches to a length of . Determine the spring constant.

Possible Answers:

Correct answer:

Explanation:

Determine the net forces on the submarine:

Plug in values:

Determine what forces are acting on the submarine:

Plug in values

*Note: Acceleration due to gravity is going down so it is a negative

Solve for :

Example Question #14 : Spring Force

Two identical, massless, springs are placed in series. A mass of  is hung from them. After all oscillations have stopped, the total length is . Calculate the spring constant of an individual spring.

Possible Answers:

Correct answer:

Explanation:

Each spring will be subject to the same force, and since they have the same spring constant, stretch the same amount. Thus:

Total stretch:

Stretch of one spring:

Use Hooke's law:

The force will be equal to the force of gravity on the mass:

Solve for :

Example Question #12 : 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 .

How would much would these stretch if instead both springs were used to attach a box of mass to the ceiling?

Possible Answers:

Correct answer:

Explanation:

The force of the spring in relationship to strain is independent of direction. Thus, the same force pulling on the spring would result in an equal amount of length change, albeit by stretching instead of compressing.

Example Question #11 : 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 .

What would the compression be if the mass were instead ?

Possible Answers:

Correct answer:

Explanation:

In this problem the "spring within a spring" can be treated as a single spring.

Use Hooke's law:

Plug in values:

Solve for .

Again use Hooke's Law:

Plug in values:

Solve for

Example Question #14 : 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 .

What is the spring constant of the combined system?

Possible Answers:

Correct answer:

Explanation:

In this problem the "spring within a spring" can be treated as a single spring.

Use Hooke's law:

Plug in values and solve for the spring constant:

Example Question #16 : 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 potential energy being stored in the springs.

Possible Answers:

Correct answer:

Explanation:

In this problem the "spring within a spring" can be treated as a single spring.

Use Hooke's law:

Convert to meters and plug in values:

Solve for

Use the equation for the potential energy stored in a spring:

Example Question #151 : Specific Forces

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 #152 : Specific Forces

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 #21 : 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 #154 : Specific Forces

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:

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