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A solid absorbs heat by radiation at 4 kW and also generates heat internally at 1.7 kW, while losing heat by convection at 5.2 kW. If the average temperature of the solid rises at 0.5 deg C per second, find the heat capacity of the solid.

1. 0.5 kJ/deg C
2. 1.0 kJ/deg C
3. 2.0 kJ/deg C
4. 5.2 kJ/deg C

Correct answer: 1.0 kJ/deg C

Solution

Net power = 4 + 1.7 - 5.2 = 0.5 kW, and with dT/dt = 0.5 deg C/s, C = 0.5 kW / 0.5 = 1.0 kJ/deg C.

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