A-LevelPhysicsForces, density and pressure9702/12 · May/June 2017 · Q101 Mark
A metal cylinder is suspended vertically in equilibrium by a cord. The diagram shows the cylinder in four different positions P, Q, R and S. [Figure shows a metal cylinder suspended in water by a cord, with tension T. Four positions are shown: P (fully submerged), Q (partially submerged, deeper), R (partially submerged, shallower), S (just above water surface).] Which statement explains the variation of the tension T in the cord?
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AAt P and at Q, the tension T in the cord is the same because the difference in pressure between the top and bottom of the cylinder is the same.
BAt Q, the tension T in the cord is less than at P because, at smaller depth, liquid pressure is smaller.
CAt R, the tension T in the cord is less than at P because atmospheric pressure is less than water pressure.
DAt S, the tension T in the cord is greater than at P because atmospheric pressure at S exerts no force on the top or bottom of the cylinder.
✓ Correct answer
A: At P and at Q, the tension T in the cord is the same because the difference in pressure between the top and bottom of the cylinder is the same.
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