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 3000°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 0°C is mixed with 50g of water at 80°C, what will be the final temperature of a mixture?
A.
0°C
B.
40°C
C.
60°C
D.
4°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 = mc∆T=50×1×80=4000cal Heat given by water is just sufficient to melt the whole ice. So the final temperature is 0°C.
