I notice that the answers are posted for the “Presidential Physics quiz” in the NY Times (original quiz wording) and, well, blech. Sorta. I’ve read decent things about the Physics for Future Presidents book, but I don’t want this to be the example for “how to quiz presidents and justify the answers.”

QUESTION 1. How does the amount of energy per gram of TNT compare with the energy per gram of a chocolate chip cookie?

My answer is (d), the cookie contains nearly 10 times as much energy.

But the answer is really around 5 or 6, depending on what numbers you’ve used, and one of the other choices is “about the same.” If you’re going to do multiple-choice, try not to bracket the right answer this way.

I do like the defense of discounting the E=mc² answer, because it shows recognition that we’re dealing with chemical rather than nuclear reactions. But in the defense of the answer, there’s

TNT explodes all by itself, no air needed.

Well, no, not really. If you balance the reaction, you’ll find that significant oxygen is needed. Sugars have oxygen in them, too. You still need external oxygen for that reaction as well.

But all of this ignores that science isn’t just a bunch of facts. What I’d rather see from a president (or student) is some reasoning, like “these are both basically combustion reactions, so to first order, I’d expect them to release similar amounts of energy” and worry about the details later on, like what difference there is because you have some nitrogen in TNT, and how that might affect the bottom line, and maybe the reasoning that you give up some energy for the convenience of a reaction that forms more moles of gases (and those gases want to occupy 22.4L each at STP, so boom!) instead of keeping the molar amount of gas the same (swapping CO2 for O2).

QUESTION 2. Based on the answer to the previous question, suggest an energy-efficient way to destroy a car.

How about letting it sit there and rust/decompose on its own? No energy input at all. The question is really open-ended; it’s a fishing expedition for what you already had in mind.

QUESTION 3. To generate the electric power of a large nuclear-power plant (1 gigawatt), how much land on a sunny day would an array of solar cells (at 40% efficiency) have to cover?

He deals with the issue of 40% panels — they exist but aren’t produced in great volume, but since ~20% panels are widely available, why no go with those? This one seems to hinge on knowing that about 1 kW per square meter of solar is available … when the sun is directly overhead. Oops. So you’re close for the southern part of the US at lunchtime during the latter two weeks of June, but pretty far off if it’s Montana around Christmas. You need to adjust for the angle of the sun (latitude and time of day)

But more to the point, power is the wrong metric to be used, since what you want to know is how much energy you can produce, and because of the factors just mentioned, for solar (unlike nuclear) you can’t just multiply that power rating by time.

QUESTION 4. Why aren’t more solar power plants being built?

Because our government hasn’t removed their collective heads from their collective place where the sun doesn’t shine (hint: I don’t mean “coal mine”) and passed some legislation that will move solar forward. Solar can be huge, and is on the cusp of becoming cost-competitive with less-desirable forms of electricity generation. What it needs in the US is a push to get it there, and allow the economies of scale (and perhaps some additional R&D advances) to make it there on its own.

Bonus question that should be (or have been) asked:

Explain why hydrogen is not really a fuel source, nor currently a GHG emissions-free fuel.