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JAMB Physics 1993 Question 13

Question 13

Density and Upthrust

An object of mass 400g and density 600 kg m−3 is suspended with a string so that half of it is immersed in paraffin of density 900 kg m−3. The tension in the string is

  1. A.1.0 N
  2. B.3.0 N
  3. C.4.0 N
  4. D.5.0 N
Show the answer and explanation

Answer: A (1.0 N)

Explanation

Volume = 0.4/600 m3; half of it displaces 900 × 0.4/1200 = 0.3 kg of paraffin, so upthrust = 3 N. Weight = 4 N, so tension = 4 − 3 = 1.0 N (g = 10 m s−2).