An object weighs 30N in air and 21N in water. The weight of the object when completely immersed in a liquid of relative density 1.4 is?

A. 25.2N
B. 17.4N
C. 12.6N
D. 9.0N

Correct Answer:

Option B – 17.4N

Explanation

Weight of water displaced = upthrust = 30 – 21 = 9N

Mass of water displaced = 9/10 = 0.9kg

Volume of object = 9 × 10^−4m³
= (9 × 10^−4) (1.4 ×10³)

= 1.26kg = 12N

30 – 12.6 = 17.4N