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Imagine a 5 m long lever. The lever is suspended by a pivot which is located at a distance of 3 m from one end. If a force of 400 N is pulling down on the long end of the lever, which force is necessary on the short end to obtain equilibrium?
  • A
    600 N.
  • B
    400 N.
  • C
    800 N.
  • D
    200 N.

For the plank to be in balance the clockwise moments must equal the anti-clockwise moments.

A moment is a mass x the balance arm.
Let X = the unknown load.

400 N x 3 m = X x 2 m
transpose to find X
400 N x 3 m ÷ 2 m = X
1200 Nm ÷ 2 m = 600 N

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