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An object weighs 30N in air and 21N in water. The weight ...

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 is B

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

  Mass of water displaced = \(\frac{9}{10}\) = 0.9kg

  Volume of object = 9 × 10\(^{-4}\)m\(^3\)

  = (9 × 10\(^{-4}\)) (1.4 ×103)

 = 1.26kg = 12N

  30 - 12.6 = 17.4N