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

Correct Answer:

Option D – 40g

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