An electric heater supplies heat to a system at a rate of 100W. If system performs work at a rate of 75 joules per second. At what rate isthe internal energy increasing?

Explanation

We are given:
  Heat supplied per second, dQ-100 W - 100 J/s
Useful work, dW = 75 J/s.
We are to calculate, Rate of increase in internal energy.
  Increase in internal energy per second, i.e. U
Using relation: `dQ = dU + dW rArr d U = d -dw-100 - 75`
`dU = 25 J//s  25W`.