JAMB - Physics (2002 - No. 1)
A copper cube weighs 0.25 N in air, 0.17N when completely immersed in paraffin oil and 0.15 N when completely immersed in water.The ratio of upthrust in oil to upthrust in water is
3 : 5
4 : 5
7 : 10
13 : 10
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 = 0.25 - 0.17 = 0.08
Ratio of upthrust in oil to upthrust in water
= \(\frac{0.08}{0.10}\) = \(\frac{8}{10}\) = \(\frac{4}{5}\) Or 4 : 5
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 = 0.25 - 0.17 = 0.08
Ratio of upthrust in oil to upthrust in water
= \(\frac{0.08}{0.10}\) = \(\frac{8}{10}\) = \(\frac{4}{5}\) Or 4 : 5
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