# Review of miscellaneous assignments

### Combustion comparison

Fuel$CO_2$ emissions (g/cal)
hydrogen 0.0
natural gas (methane) 0.21
gasoline (~octane) 0.29
coal (~ pure carbon) 0.56

And you found that

• Coal is becoming somewhat more expensive,
• Oil is becoming more expensive,
• Natural gas is getting cheaper.

### Student power

Typical results were 100-550 Watts

### Soap drop

in which we estimated the thickness of a puddle of soap to get an idea of about how big a molecule is. Biggest issues were...

• The puddle diameter was 115 mm $\Rightarrow r=$57.5 mm.
• You set the volume of the drop $V_d$ equal to the volume of the puddle $A\cdot t$, and solve for $t$. Make sure all the measurements are in the same units.
• Finally convert the thickness $t$ to meters.