Work is the amount of energy transferred into or out of a system when an applied force displaces an object.

When does a force do negative work on an object?

When the force is applied in the opposite direction to the object's motion, so the object's speed decreases .

Define conservative force .

A conservative force is a force that conserves mechanical energy within a system.

What does it mean to say that the work done by a conservative force is path-independent ?

The work done depends only on the initial and final positions of the system, not on the path taken between them.

What is the work done by a conservative force when a system returns to its initial configuration?

The work done is zero , so the change in potential energy of the system is also zero.

The work done by a nonconservative force depends on the .......... taken between the initial and final positions.

The work done by a nonconservative force depends on the path taken between the initial and final positions.

True or False? Work cannot be negative because it is a scalar quantity.

False. A scalar has no direction, but it can still be positive, negative or zero .

Name two examples of nonconservative forces .

Friction Air resistance These dissipate energy to the surroundings.

When a force acts at an angle between 90° and 180° to the displacement, the work done is .......... and the object's speed decreases.

When a force acts at an angle between 90° and 180° to the displacement, the work done is negative and the object's speed decreases.

True or False? A force applied to an object always does work on it.

False. If the object is not displaced , no work is done, however large the force.

What does the area under a force-versus-displacement graph represent?

The work done by the force, using the component of the force parallel to the displacement.

AP®PhysicsCollege BoardPhysics 1: Algebra-BasedFlashcardsUnit 3: Work, Energy & PowerWork

Work (College Board AP® Physics 1: Algebra-Based): Flashcards

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FrontDefining Work & Work Done
Define work.

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Cards in this collection (14)

Define work.
Work is the amount of energy transferred into or out of a system when an applied force displaces an object.
When does a force do negative work on an object?
When the force is applied in the opposite direction to the object's motion, so the object's speed decreases.
Define conservative force.
A conservative force is a force that conserves mechanical energy within a system.
What does it mean to say that the work done by a conservative force is path-independent?
The work done depends only on the initial and final positions of the system, not on the path taken between them.
What is the work done by a conservative force when a system returns to its initial configuration?
The work done is zero, so the change in potential energy of the system is also zero.
The work done by a nonconservative force depends on the .......... taken between the initial and final positions.
The work done by a nonconservative force depends on the path taken between the initial and final positions.
True or False?
Work cannot be negative because it is a scalar quantity.
False.
A scalar has no direction, but it can still be positive, negative or zero.
Name two examples of nonconservative forces.
- Friction
- Air resistance
These dissipate energy to the surroundings.
State the equation for work done by a constant parallel force.
$W = F d$
- $W$ = work (N·m)
- $F$ = applied force parallel to the displacement (N)
- $d$ = displacement (m)
State the equation for work done by a constant force at an angle.
$W = F_{∥} d = F d cos θ$
- $W$ = work (N·m)
- $F$ = applied force (N)
- $d$ = displacement (m)
- $θ$ = angle between the force and the displacement (°)
Why does a perpendicular force do no work?
Only the component of the force parallel to the displacement contributes to work. A perpendicular force has no parallel component ( $cos 90 ° = 0$ ), so the object's kinetic energy does not change.
When a force acts at an angle between 90° and 180° to the displacement, the work done is .......... and the object's speed decreases.
When a force acts at an angle between 90° and 180° to the displacement, the work done is negative and the object's speed decreases.
True or False?
A force applied to an object always does work on it.
False.
If the object is not displaced, no work is done, however large the force.
What does the area under a force-versus-displacement graph represent?
The work done by the force, using the component of the force parallel to the displacement.

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