Work 1 - Intro

The meaning of the word WORK in this chapter must not be confused with the general meaning of the word WORK, such as to go to work, or to work hard at playing soccer.

We calculate the amount of WORK done on an object by using an equation. (There are actually many equations to calculate WORK, so begin at the first one.)

Question 1
Study this diagram which shows a force F = 10N being applied to a box, and the box is thus moved 8m.

Diagram 1
Calculate the WORK done by this force on the box.

To do this we have an equation:

W = work done
F = force used
Δx = distance moved by that force
cosΘ = angle from the horizontal

In all the question in this section, Θ = 0, meaning the force is horizontal. Since cos0 =1, we will just leave out the cosΘ.
The equation is thus:

Solution 1

Question 2
The applied force of 20N is brought about by an electric motor. The friction force is 5N because the ground is rough. The box is moved a distance of 12m.

Diagram 2
Notice that there are THREE forces available now :
20N, 5N and the resultant force of 15N.
Hence there would be "THREE TYPES OF WORK" that can be calculated. Choose the appropriate force.

2.1. Calculate the work done by the electric motor.
The force from the motor is 20N, hence use 20N in the equation.

2.2. Calculate the work done by friction.
Friction force is 5N.

2.3. Calculate the effective work done by the motor.
The purpose of the motor was to move the box. So this means we calculate what happened to the actual box. Use the resultant force.
FR = 20 - 5 = 15N (right)

This diagram shows the relationship between the various "WORKS".

Diagram 3
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