Q. A sphere, a cube and a thin circular plate have the same mass and are made of the same material. All of them are heated to the same temperature. The rate of cooling is

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Solution:

Since the material is same, the density is same.
Since mass is same and density is same so all three have same volume.
For same volume, the surface area of plate is the largest and of the sphere is the smallest. The rate of loss of heat by radiation is proportional to surface area.