Flashcards in Work, Energy, and Momentum Deck (17):

1

## Work

### When a constant force acts on a body to move it a certain distance: W = F d cosθ, where θ is the angle between F and d. Note, when the force and displacement are perpendicular, the work done is zero, so centripetal force does no work. Units: Joule = N m = kg m^2/ s^2

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## Power

### Power is the rate of work or rate of change of energy, where P = W/ Δt with units Watt = J/ s = N m/ s = kg m^2/ s^3

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## Kinetic Energy

### Energy of an object in motion, where KE = 1/2 mv^2, with units of Joule = N m = kg m^2/ s^2

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## Potential Energy

### The energy of an object dependent upon its position, where U = mgh and U = 1/2 kx^2 (springs), with units of Joule = N m = kg m^2/ s^2

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## Total Mechanical Energy

### E = KE + U, mechanical energy is not conserved when friction is present

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## Nonconservative Force

### A force whose work depends on the path taken, such as friction

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## Conservative Force

### A force whose work is independent of the path taken, such as gravity, spring forces, and electrostatic forces

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## Work-Energy Theorem

### W = ΔKE = KE(final) - KE(initial)

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## Conservation of Energy

###
W(done by nonconservative forces) = ΔE = ΔKE + ΔU

In the presence of a nonconservative force, E(initial) > E(final)

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## What is the significance of and which equations would you use in a pulley system?

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Pulley systems allow for the same amount of work to be done by exerting a smaller force over a greater distance.

Efficiency = W(out)/ W(in) = (Load X Load Distance)/ (Effort X Effort Distance)

The distance through which the effort must move is equal to how much the supporting ropes must shorten.

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## Momentum

### A vector quantity: p = mv, with units kg m/ s = N s

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## Impulse

### J = F t = mv(final) - mv(initial) = Δp, with units kg m/ s = N s

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## Conservation of Momentum

### When no net external forces on a system, then p(initial) = p(final), therefore Δp = 0

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## Completely Inelastic Collision

### The bodies stick together after colliding, where p conserved, but KE(initial) > KE(final)

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## Completely Elastic Collision

### When p and KE (KE(initial) = KE(final)) conserved

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## Center of Mass

### X = (m1x1 + m2x2)/ (m1 + m2) in all coordinates

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