Unit 3: Work, Energy & Power

Question 1

Parallel Force

Answer 1

A force in the same or opposite direction (θ = 0° or 180°)

Question 2

Mechanical Work (W)

Answer 2

Force displacing object in direction of force or component of it

Question 3

Work (W) quantity type

Answer 3

Scalar quantity

Question 4

Work (W) variables

Answer 4

• W is work done (J)
• F is applied force (N)
• Δd is displacement (m)

Question 5

Joule (J) unit in fundamental units

Answer 5

1 J = 1 N·m = 1 kg·m²/s²

Question 6

Work (W) formula

Answer 6

W = FΔd

Question 7

Application of W = FΔd formula: Only when

Answer 7

• Applied force and displacement are in same direction
• Force on object (F) is constant

Question 8

Two-dimension analysis of work

Answer 8

Component of applied force causing displacement is required.

Question 9

Positive Work

Answer 9

• Force and displacement are in same direction
• Speed of object tends to increase

Question 10

Negative Work

Answer 10

• Force and displacement are in opposite directions
• Speed of object tends to decrease

Question 11

Zero Work

Answer 11

Situation in which no work is done on an object

Question 12

Conditions for Zero Work (only one of them is required)

Answer 12

• F = 0
• Δd = 0
• F ⊥ Δd

Question 13

Force-Position (F-d) graph

Answer 13

• x-axis: Object’s displacement (d)
• y-axis: Magnitude of force (F)
• Work = x-axis(y-axis) = FΔd

Question 14

Assumptions for F-d graphs

Answer 14

• θ = 0° or 180°
• Positive or negative work is above or below d-axis
• F can be constant or change over displacement

Question 15

When force varies in magnitude during displacement

Answer 15

• W = F(av)Δd cos θ
• F(av) is the average force across displacement

Question 16

Energy (E) [definition]

Answer 16

• The capacity (ability) to do work
• Comes in many forms

Question 17

Energy (E) [numerical quantities]

Answer 17

• Scalar quantity
• Measured in joules (J)

Question 18

Kinetic Energy, E(k)

Answer 18

Energy possessed by moving objects

Question 19

Variables of E(k)

Answer 19

• E(k) (J)
• m (kg)
• v (m/s)

Question 20

E(k) equation

Answer 20

E(k) = mv²/2

Question 21

Work-Energy Principle

Answer 21

Work done on object is related to change in kinetic energy

Question 22

Work-Energy Principle Formula

Answer 22

W(net) = ΔE(k) = E(kf) - E(ki)

Question 23

Reference Level

Answer 23

• Designated level to which objects may fall
• Considered to have gravitational potential energy of 0 J

Question 24

Potential Energy

Answer 24

Stored energy from object’s position related to forces in its environment

Question 25

Gravitational potential energy, E(g)

Answer 25

Energy possessed by object due to its position relative to Earth

Question 26

Variables for E(g) formula

Answer 26

- E(g) (J) - m (kg) - g is gravitational field strength (N/kg or m/s²) - h is height relative to a reference (m)

Question 27

Formula of E(g)

Answer 27

E(g) = mgh

Question 28

Mechanical Energy, E(mech)

Answer 28

Sum of object’s kinetic and gravitational potential energy

Question 29

E(mech) formula

Answer 29

E(mech) = E(k) + E(g)

Question 30

Types of Energy (other than the ones you already learned) [A]

Answer 30

- Chemical Potential - Elastic Potential - Electrical

Question 31

Types of Energy (other than the ones you already learned) [B]

Answer 31

- Nuclear - Radiant - Sound - Thermal

Question 32

Energy Transformation

Answer 32

Conversion of energy from one form to another

Question 33

Law of Conservation of Energy

Answer 33

- Energy is neither created nor destroyed - When energy changes from one form to another, no energy is lost

Question 34

LOCOE Formula

Answer 34

E(start) = E(during) = E(end)

Question 35

E(out)

Answer 35

Useful energy provided by a device

Question 36

E(in)

Answer 36

Energy required to operate device

Question 37

Efficiency

Answer 37

Ratio of E(out) to E(in)

Question 38

Characteristics of E(in) and E(out)

Answer 38

E(in) > E(out), E(out) < 100% in all cases

Question 39

Efficiency formula

Answer 39

efficiency = E(in)/E(out) (x 100%)

Question 40

Most common form of waste energy

Answer 40

Thermal energy

Question 41

Sankey Diagram (purpose)

Answer 41

- Diagram representing flow of energy throughout a process - ΣE(out) = E(in) (law of conservation of energy)

Question 42

Sankey Diagram (widths)

Answer 42

- Width on left represents total E(in) - Widths of arrows on right represent amount of E(in) used.

Question 43

Power (P)

Answer 43

Rate at which energy is transformed or work is done

Question 44

Power (P) formula

Answer 44

P = ΔE/Δt = W(net)/Δt

Question 45

Variables of Power Equation

Answer 45

- P is power (W) - ΔE or W(net) is work done or energy transformed (J) - Δt is the time (s)

Question 46

1 W in derived units

Answer 46

= 1 J/s = 1 N·m/s = 1 kg·m²/s³