Suppose `300J` of work done on a system and `70cal` of heat is extracted from the system. What are the values of `dW , dQ and dU` with proper signs?

Explanation

As work is done on the system, therefore `dW= -300J`
Again as `70 cal.` Of heat is extracted from the system,
`:. dQ = -70 cal. = -70xx4.2J`
Noe, `dU=dQ-dW`
`= -70xx4.2-(-300)J`
`dU= -294+300= 6J`.