# Energy & Work in Physics Flashcards

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The further the ball falls, the faster it will go because of acceleration due to gravity. This means the ball's kinetic energy will continue to increase, and will not be conserved.

*KE* = 1/2 * *mv2* = 1/2 * 95 kg * (5 m/s)2 = 1,187.5 J

The energy of a moving object

*KE* = 1/2 * mass * velocity2

Mechanical advantage = slope of inclined plane (the hypotenuse) / height from the ground

*MA* = *s* / *h*

A device that changes the direction and/or magnitude of an applied force, making it easier to do work

Examples: pulley, lever, and inclined plane

Work = force * distance

Force = mass * acceleration = 10 kg * 9.8 m/s2 = 98 N

*W* = 98 N * 5 m = 490 J

A quantity that measures the ability of something to do work

Work = force * distance = (200 + 5) * 100 m = 20,500 J

The amount an object moves in one direction due to a constant force

Calculated by multiplying force * distance

Unit: joules (J)

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## Flashcard Content Overview

In our everyday lives, we talk about work, energy, and power in different ways. In physics, however, these words have very specific definitions. These flashcards will review these definitions and describe the different calculations that can be done to describe how objects do work, use energy, and have power.

The amount an object moves in one direction due to a constant force

Calculated by multiplying force * distance

Unit: joules (J)

Work = force * distance = (200 + 5) * 100 m = 20,500 J

A quantity that measures the ability of something to do work

Work = force * distance

Force = mass * acceleration = 10 kg * 9.8 m/s2 = 98 N

*W* = 98 N * 5 m = 490 J

A device that changes the direction and/or magnitude of an applied force, making it easier to do work

Examples: pulley, lever, and inclined plane

Mechanical advantage = slope of inclined plane (the hypotenuse) / height from the ground

*MA* = *s* / *h*

The energy of a moving object

*KE* = 1/2 * mass * velocity2

*KE* = 1/2 * *mv2* = 1/2 * 95 kg * (5 m/s)2 = 1,187.5 J

The further the ball falls, the faster it will go because of acceleration due to gravity. This means the ball's kinetic energy will continue to increase, and will not be conserved.

The energy stored in an object due to its position

*PE* = mass * acceleration of gravity * height

*PE* = *mgh* = 0.500 kg * 9.8 m/s2 * 20 m = 90 J

Potential energy = 1/2 * spring constant * distance2 = 1/2 * 400 * (0.05)2 = 0.5 J

*mgh* = 1/2 * *mv2*

*m* * 9.8 * *h* = 1/2 * *m* * (15)2

*h* = 112.5*m* / 9.8*m* = 11.5 m

*GPE* = 0.005 kg * 9.8 m/s2 * 5 m = 0.245 J

*ME* = *KE* + *GPE* = 0.245 J + 0.35 J = 0.595 J

*KE* when *GPE* is 0 = 0.595 J = 1/2 * 0.005 * *v*2*
*

v* = 15.4 m/s*

*x* component of speed = 50 * cos(45°) = 35.4 m/s

*KE* = 1/2 * 15 kg * (35.4 m/s)2 = 9,399 J

*PE*is measured to be 100 J. At the bottom of the ramp, the

*KE*is measured to be 95 J. Explain the energy loss.

As the box slides down, friction converts some of the energy into heat (waste).

*ME* = *KE* + *PE*

At rest, *KE* = 0 and *GPE* = *mgh* = 10 * 9.8 * 15 = 1,470 J

*ME* = 0 + 1,470 J = 1,470 J

If no friction, *ME* is conserved and = 1,470 J at all heights

Power = work done / time interval

1 watt = 1 J/s

30 min * 60 s / 1 min = 180 s

*P* = 100 watts / 180 s = 0.56 J

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Physics 101: Intro to Physics20 chapters | 167 lessons | 11 flashcard sets

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