A copper cube weighs 0.25 N in air; 0.17N when completely immersed in paraffin oil and 0.15N when completely immersed in water. The ratio of upthrust in oil to upthrust in water is?

A. 3 : 5
B. 4 : 5
C. 7 : 10
D. 13 : 10

Correct Answer:

Option B = 4 : 5

Explanation

Wt. in air = 0.25 N
Wt.in water = 0.15 N
therefore lost in wt. in water = Upthrust in water
= 0.25 – 0.15
= 0.10 N.
Wt. in paraffin oil = 0.17 N.
.. loss in wt.in oil = upthrust in the oil
Ratio upthrust in oil to upthrust in water
= 0.18/0.10 = 8/10 = 4/5 Or 4 : 5