Find Δ U for a gas in each case, and say whether it gets warmer or cooler.

Step 1. (a) $650\ \text{J} - 240\ \text{J} = +410\ \text{J}$: warmer.

Step 2. (b) $-155\ \text{J} - 115\ \text{J} = -270\ \text{J}$: cooler. It loses heat and does work.

Step 3. (c) $0 - (-170) = +170\ \text{J}$: warmer, squeezed with no heat out.

Step 4. (d) $280\ \text{J} - 0\ \text{J} = +280\ \text{J}$: warmer, heated in a rigid tank.