A block of material of volume 20cm-3 and density 2.5gcm-3 is suspended from a spring balance with half the volume immersed in water. What is the reading of the spring balance? (Density of water = 1.0gcm-3).

  • A 8g
  • B 25g
  • C 30g
  • D 40g
  • E 50g
waec 1989physics

The correct answer is D. 40g

W = pvg = (2.5 x 10 x 60)/100 = 0.500N.

Upthrust = wt of liquid displaced = pvg water.

pvg water = (1x20x10)/2 = 0.10N

Reading => 0.500N - 0.100N = 0.4N = 40g

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