Chapter 3: Work, Energy, and Momentum

Question 1

Energy

Answer 1

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

Question 2

Kinetic Energy

Answer 2

The energy of motion

Question 3

Objects with mass and some form of velocity will have:

Answer 3

Kinetic Energy

Question 4

Kinetic Energy Equation

Answer 4

KE = ½mv²

Question 5

The SI Unit for Kinetic Energy is:

Answer 5

Joules (J)

Question 6

If velocity doubles, kinetic energy will:

Answer 6

quadruple (assuming the mass is constant)

Question 7

Potential Energy

Answer 7

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

Question 8

Potential Energy Equation

Answer 8

PE = mgh

Question 9

Total Mechanical Energy is:

Answer 9

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

Question 10

Total Mechanical Energy (E) Equation

Answer 10

E = PE + KE

Question 11

The First Law of Thermodynamics states:

Answer 11

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

Question 12

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:

Answer 12

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

Question 13

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

Answer 13

is not conserved

Question 14

Work Done by Nonconservative Forces (W’) Equation

Answer 14

W’ = ΔE = ΔKE + ΔPE

Question 15

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

Answer 15

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.

Question 16

Mechanical Energy is conserved when:

Answer 16

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

Question 17

Work is:

Answer 17

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

Question 18

Work (W) Equation

Answer 18

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)

Question 19

In the Work equation, Θ is:

Answer 19

the angle between the displacement and force vectors

Question 20

Power

Answer 20

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

Question 21

Power (P) Equation

Answer 21

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

Question 22

SI Unit of Power

Answer 22

Watts (W)

Question 23

The Work-Energy Theorem states:

Answer 23

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

Question 24

Work-Energy Theorem Equation

Answer 24

W_net = ΔK = K_f - K_i

Question 25

Momentum is defined as:

Answer 25

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.

Question 26

Momentum (p) Equation

Answer 26

p = mv (where m = mass and v = velocity)

Question 27

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

Answer 27

the vector sum of the individual momenta

Question 28

Inertia

Answer 28

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

Question 29

Impulse is defined as:

Answer 29

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

Question 30

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

Answer 30

I = FΔt = Δp = mv_f - mv_i (where I = impulse, t = time; p = momentum; m = mass; v = velocity)

Question 31

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

Answer 31

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)

Question 32

Conservation of momentum means that:

Answer 32

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

Question 33

Conservation of momentum occurs when:

Answer 33

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

Question 34

Conservation of Momentum Equation for elastic and inelastic collisions

Answer 34

m_av_ai + m_bv_bi = m_av_af + m_bv_bf

Question 35

The three types of collisions for which momentum is conserved:

Answer 35

Completely Elestic Collisions; Inelastic Collisions; Completely Inelastic Collisions

Question 36

Completely Elastic Collisions occur when:

Answer 36

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

Question 37

Conservation of Kinetic Energy in a Completely Elastic Collision Equation

Answer 37

½m_av_ai² + ½m_bv_bi² = ½m_av_af² + ½m_bv_bf²

Question 38

In completely elastic collisions:

Answer 38

kinetic energy and momentum are BOTH conserved

Question 39

Inelastic Collisions occur when:

Answer 39

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

Question 40

In inelastic collisions:

Answer 40

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

Question 41

Inelastic Collision Equation

Answer 41

½m_av_ai² + ½m_bv_bi² \> ½m_av_af² + ½m_bv_bf²

Question 42

Completely Inelastic Collisions occurs when:

Answer 42

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

Question 43

In completely inelastic collisions:

Answer 43

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

Question 44

Conservation of Momentum Equation for completely inelastic collisions

Answer 44

m_av_ai + m_bv_bi = (m_a + m_b)(v_f)

Question 45

In completely elastic collisions, what is conserved?

Answer 45

KE and momentum

Question 46

In completely inelastic collisions, what is conserved?

Answer 46

momentum; KE is lost

Question 47

In inelastic collisions, what is conserved?

Answer 47

momentum; KE is lost

Question 48

Mechanical Advantage

Answer 48

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.

Question 49

Mechanical Advantage Equation

Answer 49

Mechanical Advantage = F_out / F_in (Fout = the force exerted on an object by a simple machine; Fin = the force actually applied on the simple machine)

Question 50

Mechanical Advantage is the ratio of:

Answer 50

the force exerted on an object by a simple machine (F_out) to the force actually applied on the simple machine (F_in)

Question 51

Mechanical Advantage comes at the expense of:

Answer 51

increasing the distance over which the work is done

Question 52

Mechanical Advantage: load

Answer 52

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

Question 53

Mechanical Advantage: effort

Answer 53

the force applied to the simple machine in mechanical advantage

Question 54

Mechanical Advantage: Load Distance

Answer 54

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

Question 55

Mechanical Advantage: Effort Distance

Answer 55

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.

Question 56

Efficiency of a Simple Machine Equation

Answer 56

Efficiency = W_out / W_in = (load)(load distance) / (effort)(effort distance)

Question 57

Efficiencies are expressed as:

Answer 57

Percentages

Question 58

The efficiency of a machine gives a measure of:

Answer 58

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

Question 59

The six devices considered to be classic simple machines:

Answer 59

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

Question 60

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

Answer 60

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

Question 61

Center of Mass

Answer 61

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

Question 62

Center of Mass Equation

Answer 62

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)

Question 63

Center of Gravity Equation

Answer 63

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)