Question

A piston in a heat engine does 500 joules of work, and 1400 joules of heat are added to the system. Determine the change in internal energy and explain how this example demonstrates the conservation of energy.

Answer 1

Answer : The change in internal energy is, 900 Joules.

Solution : Given,

Heat given to the system = +1400 J

Work done by the system = -500 J

Change in internal energy is equal to the sum of heat energy and work done.

Formula used :

$\Delta U=q+w$

where,

$\Delta U$ = change in internal energy

q = heat energy

w = work done

As per question, heat is added to the system that means, q is positive and work done by the system that means, w is negative.

Now put all the given values in the above formula, we get

$\Delta U=(+1400J)+(-500J)=900J$

Therefore, the change in internal energy is 900 J.

The change in internal energy depends on the heat energy and work done. As we will change in the heat energy and work done, then changes  will occur in the internal energy. Hence, the energy is conserved.