I need help! I cannot seem to figure out what I will need to do for my final tomorrow. I will be given a mass of a glider and an acceleration. Another mass (my unknown) will be tied to a string to the glider and will graphically give me my acceleration. How do I find the mass of the unknown only given acceleration and the mass of the glider?! The only equation I learned for this was a= mg/(M+m) where m is my unknown, so this doesn't help.

excuse me? One of the most fundamental identities is

F = ma