Thread: Tell me how to calculate these two astronomy questions

I just checked my method. If you do what I said you end up with the formula

t = sqrt2 * pi * (d^3 * G^-1 * m^-1)^(1/2).

Plugging in the variables you get the answer 1.16 years.

I think it's much better to do it my way because I didn't have to memorise any highly specific formulae or anything, I just worked it out from basic physics (namely centripetal force = mv^2/r, gravitational force = G(m1)(m2)/r^2). I've never studied astronomy.

If you just ask your professor what formula is required and then put in the numbers, that's just a lesson in how to use a calculator. It's not really physics and it won't help you to study for an exam.

Also, be careful with your significant figures. Were the original data written as '3' or '3.00'? If it was the former then you can only give your final answer to at most 2 significant figures, if it was the latter you should give it to 3. Those final digits you wrote down are meaningless, as the '3' you are initially given, if that's how it was originally given, represents a pretty massive potential error as the real figure could be anywhere between 2.5 and 3.5.

Remember, as a general rule, only give your answer to the least number of significant figures in the original data. There could well be marks for understanding this.

I appreciate your help, I really do.

Took the test. Think I did quite well. Luckily, because this is astronomy, the class doesn't focus heavily on physics. As such, the teacher emphasized the actual mathematical process itself and gave us the formulas and values for things like the speed of light. It was actually quite an easy test so long as you read the chapters. I now realize the worry that instigated this thread was unjustified. Although, I am glad I have this thread for future reference.

No problem.

Well done on the test.