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JAMB Physics 2019 Question 14

Question 14

Equilibrium of Forces

A uniform metre rule QR is balanced on a knife edge which is 55cm from R. When a mass of 10g is hung at P as shown below, the mass of the metre rule is

Diagram for this question
  1. A.70g
  2. B.350g
  3. C.550g
  4. D.35g
Show the answer and explanation

Answer: A (70g)

Explanation

The pivot is 45 cm from Q and the 10 g mass hangs 10 cm from Q, i.e. 35 cm from the pivot. The rule's weight acts at 50 cm, 5 cm the other side. 10 × 35 = m × 5, so m = 70 g.