A block of material of volume 20cm-3 and density 2.5gcm-3 is suspended from a spring...

WAEC 1989

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

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Correct Answer: Option D

Explanation

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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