Question

which of the following circumstances leads to a loss of internal energy of a system?

A. 600 J of heat is removed from a system that has 700 J of work done on it
B. 600 J of heat is removed from a system that has 600 J of work done on it
C. 100 J of heat is added to a systsem that has 600 J of work done of it
D. 100 J of heat is added to a system that does 600 J of work

Answer 1

here we have to apply this formula, namely the first principle of thermodynamics:
\[Q = \Delta U + W\]

Answer 2

ok! how do we do that?

Answer 3

we have to pick the case for which \Delta U < 0

Answer 4

ok! not sure which that would be :(

Answer 5

for example, I consider the case A:
there we have:
Q= -600 and W= -700 so substituting, we get:
\[\begin{gathered}
- 600 = \Delta U - 700 \hfill \\
\Delta U = 100Joules \hfill \\
\end{gathered} \]
so the answer can not be case A

Answer 6

ohh i see so should it be choice C? :/

Answer 7

case B:
Q=-600, W= -600, so \Delta U=0
so it is not case B

Answer 8

yes:)

Answer 9

case C;:
Q= +100, W= -600
so: \Delta U= 700
so it is not case C

Answer 10

ohh oops :P so it is choice D?

Answer 11

yes! since case D:
Q= 100, and W= 600, so:
\Delta U = 100-600=-500 which is negative

Answer 12

ooh yay!! thank you!!

Answer 13

thank you!! :)