3.3 Work, Energy, and Power

Question 1

What is work done and state its unit

Answer 1

Energy transferred as a product of force applied and distance moved by an object in the direction of the force

Joules (J) or Newton metres (Nm)

Question 2

What are forms of energy are stores

Answer 2

• chemical
• kinetic
• elastic potential
• gravitational potential
• thermal
• nuclear

Question 3

What forms of energy are transfers

Answer 3

• mechanical
• radiation
• electrical

Question 4

What is the equation for kinetic energy

Answer 4

Kinetic energy (J) = 0.5 x mass (kg) x velocity² (ms^-1)

KE = 0.5mv²

Question 5

What s the equation for GPE

Answer 5

GPE (J) = mass (kg) x acceleration due to gravity (ms^-2) x height (m)

GPE = mgh

Question 6

How is energy exchanged between KE and GPE

Answer 6

All initial GPE is converted to KE as an object falls and converted back to GPE as it rises again

GPE = KE

Question 7

What is power and state its units

Answer 7

Rate of energy transfer or rate of work done

Watts (W)

Question 8

What are the equations for power

Answer 8

Power (W) = energy transferred (J) / time (s)

P = E/t

Power (W) = force (N) x velocity (ms^-1)

P = Fv

Question 9

What is efficiency and state its unit

Answer 9

How much of the initial energy is conserved as useful energy

Percentage (%)

Question 10

What is the equation for efficiency

Answer 10

Efficiency = (useful output energy / total input energy) x 100