Problem set 15 + exam prep

Hi everyone 

Apologies for the delay for solutions to PS 15. I'll upload it sometime this week. In general, I hope the solutions have been useful in helping you learn and understand a bit of GR. 

With exam season in full swing, here are some unsolicited pieces of advice for dealing with the weeks ahead, in particular when studying for GR:  

* Get plenty of sleep, each and every day. It's a seriously underrated commodity, especially among physics students. 

* In a similar vein, don't forget to eat regularly and take walks. This year spring is a rare sunny one. I know I'm more anxious for it as a South African, but you can never have too many nice days.

* If you aren't focusing or understanding something, take it easy on yourself. Exams really up the pressure and therefore focusing can sometimes be tough. On top of that GR is *actually* hard. The occasional lack of motivation is expected, so don't sweat some dips in productivity. 

* Just try your best, whatever that may be at the moment.

Good luck for studying and for all the exams ahead!

Jake