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

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

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  • Define power.

    Power is the rate at which energy changes with respect to time.

  • State the equation for average power.

    P_{\text{avg}} = \frac{∆E}{∆t}

    • P_{\text{avg}} = average power (W)

    • ∆E = change in energy (J)

    • ∆t = change in time (s)

  • What is the unit of power?

    The watt (W)

    1 \text{ W} = 1 \text{ J/s}

  • What two kinds of energy change can power describe?

    • A transfer of energy into or out of a system

    • A conversion from one energy type to another within a system

  • Average power can also be found from the .......... done divided by the time taken.

    Average power can also be found from the work done divided by the time taken.

  • True or False?

    A machine that does more work always has a greater power.

    False.

    Power is work done per unit time. A machine doing more work over a much longer time can have a lower power.

  • Define instantaneous power.

    Instantaneous power is the power delivered to an object at an exact instant in time.

  • State the equation for instantaneous power.

    P_{\text{inst}} = F_{\parallel} v = F v \text{cos} \theta

    • P_{\text{inst}} = instantaneous power (W)

    • F_{\parallel} = component of the applied force parallel to the velocity (N)

    • F = applied force (N)

    • v = speed (m/s)

    • \theta = angle between the applied force and the velocity (°)

  • The equation P_{\text{inst}} = F_{\parallel} v applies to a .......... force parallel to the velocity.

    The equation P_{\text{inst}} = F_{\parallel} v applies to a constant force parallel to the velocity.

  • How is the equation for instantaneous power derived from the equation for work?

    • Substitute W = F_{\parallel} d into P = \frac{W}{∆t}

    • Recognize that \frac{d}{∆t} is the speed, v

    • This gives P_{\text{inst}} = F_{\parallel} v

  • True or False?

    Instantaneous power is the average power over a long time interval.

    False.

    Instantaneous power is the power delivered at an exact instant, found using the force and the speed at that instant.

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