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Kaplan Physics > Chapter 3: Work, Energy, and Momentum > Flashcards

Chapter 3: Work, Energy, and Momentum Flashcards

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1
Q

Energy

A

A property or characteristic of a system to do work / make something happen

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2
Q

Kinetic Energy

A

The energy of motion

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3
Q

Objects with mass and some form of velocity will have:

A

Kinetic Energy

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4
Q

Kinetic Energy Equation

A

KE = ½mv2

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5
Q

The SI Unit for Kinetic Energy is:

A

Joules (J)

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6
Q

If velocity doubles, kinetic energy will:

A

quadruple (assuming the mass is constant)

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7
Q

Potential Energy

A

An object that has mass and the potential to do something.

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8
Q

Potential Energy Equation

A

PE = mgh

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9
Q

Total Mechanical Energy is:

A

The sum of an object’s potential and kinetic energies.

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10
Q

Total Mechanical Energy (E) Equation

A

E = PE + KE

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11
Q

The First Law of Thermodynamics states:

A

Energy is never created or destroyed. It is merely transferred from one system to another.

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12
Q

When the work done by nonconservative forces is zero (when there are no nonconservative forces acting on the system), the total mechanical energy of the system:

A

remains constant. (E = PE + KE = Constant)

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13
Q

When nonconservative forces such as friction and air resistance are present, total mechanical energy:

A

is not conserved

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14
Q

Work Done by Nonconservative Forces (W’) Equation

A

W’ = ΔE = ΔKE + ΔPE

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15
Q

The work done by nonconservative forces such as air resistance and friction is exactly equal to:

A

the amount of energy ‘lost’ from the system. NOTE: the energy was not ‘lost’, it was just transferred out of the system and into another.

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16
Q

Mechanical Energy is conserved when:

A

No nonconservative forces (friction, air resistance, etc. are present).

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17
Q

Work is:

A

a process in which energy is transferred from one system to another when something exerts forces on or against something else.

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18
Q

Work (W) Equation

A

W = FdcosΘ

(F = force applied; d = displacement through which the force is applied; Θ = the angle between the applied force vector and the displacement vector)

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19
Q

In the Work equation, Θ is:

A

the angle between the displacement and force vectors

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20
Q

Power

A

The rate at which energy is transferred from one system to another.

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21
Q

Power (P) Equation

A

P = W / t (where W = work and t = time)

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22
Q

SI Unit of Power

A

Watts (W)

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23
Q

The Work-Energy Theorem states:

A

the net work done on or by an object will result in an equal change in the object’s kinetic energy.

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24
Q

Work-Energy Theorem Equation

A

Wnet = ΔK = Kf - Ki

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25
Q

Momentum is defined as:

A

a quality of objects in motion. It is defined as the product of an object’s mass times its velocity. Therefore, it is a vector quantity.

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26
Q

Momentum (p) Equation

A

p = mv

(where m = mass and v = velocity)

27
Q

For two or more objects, the total momentum is equal to:

A

the vector sum of the individual momenta

28
Q

Inertia

A

the tendency of objects to resist changes in their motion and momentum

29
Q

Impulse is defined as:

A

the change in an object’s momentum. It is a vector quantity.

30
Q

For a constant force applied through a period of time, impulse and momentum are related by this equation:

A

I = FΔt = Δp = mvf - mvi

(where I = impulse, t = time; p = momentum; m = mass; v = velocity)

31
Q

The longer the time of change in momentum (Impulse), the smaller the:

A

Force necessary to achieve the impulse. (Example - Crush zones in cars. The longer amount of time the car crushes, the smaller the force felt on the occupancy zone by the change in momentum - the change in momentum occurs over a longer period of time, and thus the force felt is smaller)

32
Q

Conservation of momentum means that:

A

the momentum after a collision is the same as the momentum before the collision.

33
Q

Conservation of momentum occurs when:

A

No nonconservative forces (friction, air resistance, etc. are present).

34
Q

Conservation of Momentum Equation for elastic and inelastic collisions

A

mavai + mbvbi = mavaf + mbvbf

35
Q

The three types of collisions for which momentum is conserved:

A

Completely Elestic Collisions; Inelastic Collisions; Completely Inelastic Collisions

36
Q

Completely Elastic Collisions occur when:

A

Two or more objects collide in such a way that both kinetic energy and momentum are conserved. They do not stick together.

37
Q

Conservation of Kinetic Energy in a Completely Elastic Collision Equation

A

½mavai2 + ½mbvbi2 = ½mavaf2 + ½mbvbf2

38
Q

In completely elastic collisions:

A

kinetic energy and momentum are BOTH conserved

39
Q

Inelastic Collisions occur when:

A

a collision results in the decrease of kinetic energy of the system through the production of sound, heat, light, etc.

40
Q

In inelastic collisions:

A

momentum is conserved, but the final kinetic energy is LESS THAN the initial kinetic energy

41
Q

Inelastic Collision Equation

A

½mavai2 + ½mbvbi2 > ½mavaf2 + ½mbvbf2

42
Q

Completely Inelastic Collisions occurs when:

A

objects collide and stick together rather than bouncing off each other and moving apart.

43
Q

In completely inelastic collisions:

A

momentum is conserved, but the final kinetic energy is LESS THAN the initial kinetic energy

44
Q

Conservation of Momentum Equation for completely inelastic collisions

A

mavai + mbvbi = (ma + mb)(vf)

45
Q

In completely elastic collisions, what is conserved?

A

KE and momentum

46
Q

In completely inelastic collisions, what is conserved?

A

momentum; KE is lost

47
Q

In inelastic collisions, what is conserved?

A

momentum; KE is lost

48
Q

Mechanical Advantage

A

Any device (such as an inclined plane) that allows for work to be accomplished through a reduced applied force is said to provide mechanical advantage.

49
Q

Mechanical Advantage Equation

A

Mechanical Advantage = Fout/ Fin

(Fout = the force exerted on an object by a simple machine; Fin = the force actually applied on the simple machine)

50
Q

Mechanical Advantage is the ratio of:

A

the force exerted on an object by a simple machine (Fout) to the force actually applied on the simple machine (Fin)

51
Q

Mechanical Advantage comes at the expense of:

A

increasing the distance over which the work is done

52
Q

Mechanical Advantage: load

A

the load is the weight of an object (mg) in a mechanical advantage situation

53
Q

Mechanical Advantage: effort

A

the force applied to the simple machine in mechanical advantage

54
Q

Mechanical Advantage: Load Distance

A

the distance an object is moved by a simple machine in mechanical advantage

55
Q

Mechanical Advantage: Effort Distance

A

In a pulley system, the length of rope that must be pulled in order to move the object the load distance. Effort distance is longer than load distance.

56
Q

Efficiency of a Simple Machine Equation

A

Efficiency = Wout/ Win = (load)(load distance) / (effort)(effort distance)

57
Q

Efficiencies are expressed as:

A

Percentages

58
Q

The efficiency of a machine gives a measure of:

A

the amount of work put into the system that “comes out” as useful work

59
Q

The six devices considered to be classic simple machines:

A

inclined planes, wedges, pulleys, axle and wheel, lever, and screws

60
Q

In an idealized pulley (one that is massless and frictionless), the work put into the system is equal to:

A

the work that comes out of the system. Thus, the pulley has a 100% efficiency.

61
Q

Center of Mass

A

The point that acts as if the entire mass was concentrated at that point.

62
Q

Center of Mass Equation

A

X = m1x1 + m2x2 + m3x3 + .. / m1 + m2 + m3 ..

(where m1, m2, and m3 are the masses of three different objects and x1, x2, and x3 are there positions along the x-axis)

63
Q

Center of Gravity Equation

A

X = w1x1 + w2x2 + w3x3 + .. / w1 + w2 + w3 ..

(where w1, w2, and w3 are the weights of three different objects and x1, x2, and x3 are there positions along the x-axis)

Kaplan Physics (14 decks)

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