Work, Energy, and Momentum Flashcards Preview

MCAT Physical Sciences > Work, Energy, and Momentum > Flashcards

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

2

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

3

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

4

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

5

Total Mechanical Energy

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

6

Nonconservative Force

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

7

Conservative Force

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

8

Work-Energy Theorem

W = ΔKE = KE(final) - KE(initial)

9

Conservation of Energy

W(done by nonconservative forces) = ΔE = ΔKE + ΔU
In the presence of a nonconservative force, E(initial) > E(final)

10

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

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.

11

Momentum

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

12

Impulse

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

13

Conservation of Momentum

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

14

Completely Inelastic Collision

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

15

Completely Elastic Collision

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

16

Center of Mass

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

17

Center of Gravity

The point on some object where the entire force of gravity acts.