Answer:
The length of the moment arm is 19 cm
Step-by-step explanation:
Given;
The total length of the ruler, L = 40 cm
a mass is hung from its center mass, at 21 cm
a force, F is applied at 40 cm
The length of the moment arm is calculated as;
the center mass of the ruler is at 20 cm mark
0 21cm 40cm
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↓ r ↓
M F
Moment about F, = Fr
The length of the moment arm is = r
r = 40 cm - 21 cm
r = 19 cm
Therefore, the length of the moment arm is 19 cm