Lesson: Chapter 11 — Turning Effect of a Force

11.2. Couple of forces 8 of 12 Reset answers

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Question 8

On a thin board pivoted at O, a force of 10 N acts downwards at one end and 10 N upwards at the other. One of them is 0.4 m from O and the other 0.3 m from O. What is the moment of this couple?

A 14 N m B 20 N m C 7 N m D 3 N m

The right answer is the one marked above.

7 N m. The perpendicular distance between the lines is 0.4 m + 0.3 m = 0.7 m. moment = 10 N × 0.7 m = 7 N m.

Adding the forces to get 20 N × 0.7 = 14 N m is the trap. It is the two distances that are added, not the two forces.

Answer the question to continue.