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UNIT G481: MECHANICS
Module 3: Work and energy
1.3.1 - Work
Candidates should be able to:
 Define work done by a force
 Define the joule;
 Calculate the work done by a force using….
W = Fx and W = Fx cos θ;
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Calculating Work done
The work done by a force is the product of the
force and the distance moved in the direction of
the force.
W=Fx
W: the work done in Joules (J)
F: the force applied in Newtons (N)
x: the displacement of the object (in the direction of the
force) in metres (m)
The Joule is the unit used to measure work done
as well as ENERGY. It is defined as 1J = 1Nm.
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Work done by a force
In order to get a wooden crate into a storage container, you have
a choice of lifting it vertically or pushing it up a ramp to point A.
Using the values shown on the diagram below, state which
method you would use and use calculations to explain your
reason.
A
4m
30N
3m
30N
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My calculations
A
4m
30N
3m
30N
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A few more examples
(pay close attention to your units)
Calculate the work done to lift the given loads through the
relevant distance. Show your working.
Load
Distance
5N
40cm
0.6kN
3m
5kg
4m
750g
20mm
Work done
Unit
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Reviewing the trigonometry
1.
Sin q =
2.
Cos q =
3.
Tan q =
If given the length of the
hypotenuse, how would you
find the length of the opposite
side?
q
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Extending the equation to practical situations
A block is moved up a ramp using a pulley at the top of the ramp.
This allows someone on the floor to apply the force safely and
comfortably.
The worker pulls with a vertical force of 200N. The ramp is inclined
at an angle of 40o and is 5m long (see diagram).
How would we calculate the work done in this situation?
200N
5m
40o
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Read pages 79 – 83
Complete SAQs 1  5
Check your answers after each question