3.3 - Work, Energy and Power

Question 1

What is the verbal DEFINITION of WORK DONE?

Answer 1

The product of force and the distance moved by the force in the direction of movement.

Question 2

What is the formula for Work Done (no angle involved)?

Answer 2

Work Done = Force x Distance

Units: W - Joules (J)/ Newton metres (Nm)
F - Newtons (N)
d - Metres (m)

Question 3

1 J of work is transferred when…

Answer 3

…a force of 1 N causes an object to MOVE (not apply) a distance of 1 m in the DIRECTION of the force. (remember, force is a vector).

Question 4

If a force is at an angle to the direction of motion, what is the formula for work done?

Answer 4

W = Fcosθ d

It is the HORIZONTAL COMPONENT of the force multiplied by the distance.

Question 5

cos 90 = 0

What is the work done?

Answer 5

W = F (cos90) x d

= 0 J

Question 6

cos 0 = 1

What is the work done?

Answer 6

W = F (cos01) x d

= “Fd” J

Question 7

What are the different forms of energy?

Give an example of how each form of energy can be transferred to another form.

Answer 7

1. KINETIC, e.g. a car’s engine transfers chemical energy stored in fuel to KE.
2. GRAVITATIONAL POTENTIAL, e.g. a mountain climber gains GPE as they climb up the mountain.
3. THERMAL, e.g. the internal energy of water in a kettle increases as the heating element transfers energy to molecules of water.
4. ELASTIC POTENTIAL, e.g. the work done in sretching an elastic material is stored as EPE.
5. NUCLEAR, e.g. the energy transferred during nuclear fission comes from the mass difference between the original nucleus and the smaller fragments (mass defect)