Physics

Physics

Problem

A glass marble of mass 40 g40\,\text{g} and volume 18 cm318\,\text{cm}^{3} is gently lowered into a jar containing two immiscible liquids. The upper layer is kerosene of density 800 kg m−3800\,\text{kg\,m}^{-3} and the lower layer is glycerine of density 1260 kg m−31260\,\text{kg\,m}^{-3}. The height of the kerosene layer is greater than the diameter of the marble. a. (i) Calculate the density of the marble. b. (ii) Will the marble come to rest entirely in the kerosene layer, at the kerosene–glycerine interface, or sink into the glycerine layer? Support your answer with calculations. c. (iii) If the marble finally floats partially submerged in the glycerine layer, calculate the volume of the marble that will be below the upper surface of glycerine in its equilibrium position.
Intuitive explanation

This problem is about buoyancy and equilibrium at an interface. The marble will sink through the less dense kerosene but may float or sink in the denser glycerine depending on the balance between its weight and the buoyant forces from each liquid. The key insight is to compare the marble's density to each liquid's density: if the marble is denser than a liquid, it sinks through it; if less dense, it floats. You'll need to find where the marble settles by checking whether it can be fully supported by buoyancy in one or both layers.

Intuitive explanation

This problem is about buoyancy and equilibrium at an interface. The marble will sink through the less dense kerosene but may float or sink in the denser glycerine depending on the balance between its weight and the buoyant forces from each liquid. The key insight is to compare the marble's density to each liquid's density: if the marble is denser than a liquid, it sinks through it; if less dense, it floats. You'll need to find where the marble settles by checking whether it can be fully supported by buoyancy in one or both layers.

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