The child applies a force of 2.0 N on gear A. The perpendicular distance between the force and the pivot is 7.5 cm. Calculate the moment of the force about the pivot.
How to approach this question
1. Identify the values for force (F) and distance (d).
2. Check the units. The standard unit for distance in the moment equation is metres (m), but the question gives it in centimetres (cm). You must convert cm to m.
3. Substitute the values into the equation M = Fd.
4. Calculate the final answer and give the correct units for a moment.
Full Answer
1. Convert distance to metres: d = 7.5 cm = 0.075 m
2. Equation: M = Fd
3. Substitute: M = 2.0 N × 0.075 m
4. Calculate: M = 0.15 Nm
To calculate the moment, we use the equation M = Fd.
Given values are:
F = 2.0 N
d = 7.5 cm
First, we must convert the distance from centimetres to metres, because the standard unit for moment is the Newton-metre (Nm).
d = 7.5 cm / 100 = 0.075 m
Now, substitute the values into the equation:
M = 2.0 N × 0.075 m
M = 0.15 Nm
Common mistakes
✗ Forgetting to convert the distance from cm to m. This is a very common mistake and would lead to an answer of 15 Nm.\n✗ Calculation errors.\n✗ Using the wrong units for the final answer (e.g., N or J instead of Nm).
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