Question

First law of thermodynamics sign convention

Answer 1

The convention of your physics book is not conventional for theoretical physics, however, it is often used in engineering thermodynamics.
In physics and chemistry, one considers the change of the internal energy of the system. So if work is done on the system, work is counted positive.
Same for heat, which is positive if heat is entering the system. On the other hand enigneers are usually interested in the work done by an engine when some heat is input.
Hence they use different sign for work and heat.

Answer 2

Explanation:

First law of Thermodynamics :-

→ According to this La energy can neither be created nor be destroyed. So you in any physical or chemical process Total energy of universe is constant .

°•° ∆U = q + W.