16. Conservation of Energy

Question 1

State the principle of conservation of energy

Answer 1

Energy cannot be created or destroyed. It can be transferred from one for to another but the total amount of energy in a closed system will not change

Question 2

What is the equation for efficiency in terms of energy?

Answer 2

efficiency = useful energy output / total energy input

Question 3

What is the equation for efficiency in terms of power?

Answer 3

efficiency = useful output power / total input power

Question 4

What is the equation for kinetic energy?

Answer 4

Kinetic energy = 1/2 x mv^2

Question 5

What is the equation for gravitational potential energy?

Answer 5

GPE = mg Δh

Question 6

What is the equation for elastic potential energy?

Answer 6

EPE = 1/2 x k(ΔL)^2

k = stiffness constant (N/m)
ΔL = extension of material (m)

Question 7

What is the relationship between kinetic energy and GPE when an object falls, assuming no air resistance?

Answer 7

1/2 x mv^2 = mg Δh

The gain in kinetic energy is equal to the loss in GPE

Question 8

How can you investigate efficiency?

Answer 8

Investigate the efficiency of an electric motor as it lifts a mass through a measured vertical distance