Question

If $20kj$ of work was done by the waterfall per unit volume of water and $30kj$ of heat was lost per unit volume, the energy change per unit volume of water is:

• A. $+50kJ$
• B. $-10kJ$
• C. $-50kJ$
• D. $+10kJ$

Answer 1

Answer: (C)

$-50kJ$

$\frac{w}{v}=-20KJ$ $\left(\right(-)$because work is done by the water$)$

& $\frac{q}{v}=-30KJ$ $\left(\right(-)$because heat is lost$)$

$\therefore$ Energy change per unit volume$=\frac{△u}{v}=\frac{q}{v}+\frac{w}{v}$

$=-30-20$

$=-50KJ$