Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for_________________?
Correct answer: A. Cube
- A. Cube
- B. Cylinder
- C. Sphere
- D. Equal for all the three
Explanation
For equal masses and the same material, the object with the largest surface-area-to-volume ratio cools fastest under comparable conditions. Among these shapes, the cube has the greatest ratio, so it reaches 90% temperature change first.
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