Same material is used to make a sphere, a cube and a thin circular plate and having the same mass. They are initially heated to a temperature of 3000Â°C. Which of these will cool fast?

A.

Sphere

B.

Cube

C.

Plate

D.

All three will cool at the same rate

Answer: Option C

Explanation:

All three have the same mass and hence the same volume. Therefore the plate has a maximum surface area. So, the plate will cool fastest.

50g of ice at 0Â°C is mixed with 50g of water at 80Â°C, what will be the final temperature of a mixture?

A.

0Â°C

B.

40Â°C

C.

60Â°C

D.

4Â°C

Answer: Option A

Explanation:

Heat required to melt 50g ice = mL = 50×80=4000cal Heat given out by water in cooling from 80°C to 0 = mcâˆ†T=50×1×80=4000cal Heat given by water is just sufficient to melt the whole ice. So the final temperature is 0°C.