Question

A source supplies heat to a system at the rate of 1000 W. If the system performs work at a rate of 200 W. The rate at which internal energy of the system increases 

(1) 1200 W 

(2) 600 W 

(3) 500 W 

(4) 800 W

Answer 1

Correct option is (4) 800 W

dQ = dU + dw

\(\frac{dU}{dt}=\frac{dQ}{dt}-\frac{dw}{dt}\)

\(\frac{dU}{dt}=100-200=800W\)