# First law for a closed system undergoing a cycle

I have read two statements for first law of a closed system undergoing a cycle. One says that the net work in the cycle must be equal to net heat, so that no energy change takes place. This part i get, but then i read another article, which is obtained from joules experiment, in which the work input in a cycle is proportional to the heat rejected by a factor of J(mechanical equivalent of heat). Aren't these two statements contradictory. One says that, in a cycle net work is EQUAL to net heat, while the other, says there are proportional. Please help, i am confused.

Your constant of proportionality is the numerical link between these two units, $4.2\;\rm J \approx 1 \;calorie$.