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JAMB Physics 2008 Question 8

Question 8

Equilibrium of Forces

The diagram above shows plank RS pivoted at its centre of gravity O and is in equilibrium with the weights P and Q. If a weight 2P is added to P, the plank will be in equilibrium again by

Diagram for this question
  1. A.moving Q nearer to O.
  2. B.moving P nearer to O.
  3. C.adding a weight Q to Q.
  4. D.moving P further away from O.
Show the answer and explanation

Answer: B (moving P nearer to O.)

Explanation

The load on P's side becomes 3P, so its moment about O increases. To balance again, that moment must be reduced by moving P (now 3P) nearer to O so that 3P × new distance equals Q's moment.