3.3 Work, Energy and Power

Question 1

Define work done:

Answer 1

The product of the magnitude of the force and the distance moved by the object in the direction of the force

Unit: Joules (J)

Question 2

Define Kinetic Energy and give its SI base unit:

Answer 2

The energy associated with the motion of an object with mass

The SI base unit is kg m^2 s^-2

Question 3

Define Gravitational Potential Energy:

Answer 3

The energy of an object due to its position in a gravitational field

Question 4

Define Elastic Potential Energy:

Answer 4

The energy stored by an object as a result of a reversible change in its shape

Question 5

State the principle of conservation of energy:

Answer 5

In a closed system, energy cannot be created or destroyed but only transferred from one form to another

Question 6

If we consider a closed system where an object is moving up and down, derive a formula for the velocity of an object in a gravitational field:

Answer 6

All initial GPE is converted to KE as the object falls, and this Ke is converted back to GPE as it rises

Equating KE and GPE gives: mgh = 1/2 mv^2

Rearranging this in terms of v^2 gives:

v^2 = 2gh, so v = sqrt(2gh)

Since there is no “m” in the calculation, the mass has no effect on the final speed - the acceleration of free fall is the same for all objects

Question 7

The rate of work done is equal to…

Answer 7

Power

Question 8

What is efficiency?

Answer 8

efficiency =

(useful output power / total input power) x100