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The internal energy of a monatomic ideal gas is 1.5 nRT. One mole of helium is kept in a cylinder of cross-sectional area 8.5 cm². The cylinder is closed by a light frictionless piston. The gas is heated slowly until 42 J of heat has been supplied. The temperature rises by 2 degrees C. The distance moved by the piston can be written as alpha * 10^beta m (scientific notation). Find alpha + beta. [Take R = 25/3 J/(mol K), atmospheric pressure = 100 kPa]

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

Since the piston is frictionless and light, the process is isobaric at atmospheric pressure. First law gives W = Q - delta_U. We find W, then use W = P*A*d to get distance d.

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