15. Work and Power

Question 1

What is meant by work?

Answer 1

The amount of energy transferred from one form to another when a force causes a movement of some sort

Question 2

What is the equation for calculating work done?

Answer 2

W = Fs

W = work done (J)
F = force causing motion (N)
s = distance moved in same direction as force (m)

Question 3

Define the term joule

Answer 3

One joule is the work done when a force of 1 newton moves an object through a distance of 1 metre

Question 4

What is the equation for calculating work done at an angle?

Answer 4

W = Fs cos θ

θ = angle at which force acts from direction of motion

Question 5

Define the term power

Answer 5

The rate of doing work (i.e. the amount of energy transferred from one form to another per second)

Question 6

What is the equation for power in terms of work done?

Answer 6

P = ΔW / Δt

P = power (W)
ΔW = work done (J)
Δt = time (s)

Question 7

Define the term watt

Answer 7

The rate of energy transfer equal to 1 joule per second (J/s)

Question 8

What does the area under a force-displacement graph show?

Answer 8

Work done

Question 9

Why can’t you use the formula W = Fs for a variable force?

Answer 9

The value of F is constantly changing

Question 10

How do you find the work done for variable force?

Answer 10

Plot a force-displacement graph

Question 11

What goes on the x-axis of a force-displacement graph?

Answer 11

Displacement

Question 12

What goes on the y-axis of a force-displacement graph?

Answer 12

Force

Question 13

What equation of power is useful for moving objects?

Answer 13

P = Fv cos θ

P = power (W)
F = force causing motion (N)
v = speed in the direction of motion (m/s)
θ = angle at which the force acts from the direction of motion