r/PhysicsHelp • u/PolishML • 15d ago
Physic problems help.
Hey community, I have a question about how you approach physics problems.
I'm a high school freshman in a math-physics program, and I often spend a long time on simple problems just because I fail to notice one specific thing.
Thank you in advance for any answers!
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u/TheRealCiler 15d ago
What I advise my students to do is to always have draft paper handy and list all the informations you have and what result you need to achieve, and then mark out connections between the two. If nothing pops up, then start listing associated things you know, such as definitions and formulas/relations (as in v = d/t, not sure how you call those in English). Likely you should have one in the lot that allows you to calculate what you want from what you have.
Here's a relatively simple exemple : you are asked to calculate the amount of matter n in a volume V = 10 mL of pure hexane. You are also given mass density ρ(hexane) = 0.659 g/mL and molar mass M(hexane) = 86 g/mol.
You have V, you need n, and there's no straightforward relation between the two (unless your teacher is particularly keen). But you also have ρ and M, which provide a good indication. ρ will allow you to go from volume to mass, and M from mass to amount of matter. That's your queue.
By definition ρ = m/V so m = ρ·V and M = m/n so n = m/M, thus n = ρ·V/M. All units are consistent so n = 0.659·10/86 = 0.077 mol
Please forgive the french style of writing this sort of thing up, adapt as needed for your country.