Question

A gas is compressed at constant pressure $50N/m^2$ from a volume of $0m^3$ to a volume $4m^3.$ Energy $100J$ is then added to the gas by heating. Its internal energy is :

• A. Increased by $100J$
• B. Increased by $200J$
• C. Decreased by $100J$
• D. Increased by $400J$

Answer 1

Answer: (D)

Increased by $400J$

Change in volume $△V_2-V_1=4-10=-6m^3$

A volume decreases, work is done on the gas and so it is negative.

$W=p△V=50\times (-6)=-300J$

Additional heat supplied $(G=+100J).$ So, for the first law of thermodynamics change in external energy is given by

$△U=Q-W=100-(-300)=400J$

Internal energy increases by 400 J.