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A 3 m long plank is on a pivot (halfway along its length). A 1 kg mass is suspended on the left end and a 2 kg mass from other end.How far and in which direction should the plank be moved in order for the plank to be in balance?
  • A
    1m to the left.
  • B
    1m to the right.
  • C
    0.5m to the left.
  • D
    0.5m to the right.

Remember it's asking in which direction the blank will move not the pivot.
To make balance:
(Mass x arm) on one side of pivot = (mass x arm) on another site of pivot
Fa x arm = Fb x arm

1 x left arm = 2 x right arm
Right arm = 1/2 left arm
If total length of plank is 3 m, right arm is half of left arm:
Right arm: 1 m
Left arm: 2 m

As the pivot was in the middle of the plank so each arm was 1.5 m, so plank has to move left.

Correct Answer: 0.5m to the left.

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