Question

1. A steam engine converts 150 kg of water completely to steam. The process involves transfer of 4 x 10^8 J as heat. If steam escaping through the safety valve does 2 x 10^8 J of work against outside atmosphere, the net change in the internal energy is:
a. 2 J
b. 2 x 108 J
c. 6 J
d. 6 x 108 J

2. A steam engine absorbs 4 x 10^5 J and expels 3.5 x 10^5 J in each cycle. What is its efficiency?
a. 100%
b. 12.5%
c. 75%
d. 33%

Thank you for the help! Physics is my hardest subject. :(