I have a question about Physics...

The acceleration is given by: a = g*(m2 - m1)/(m1 + m2) where g is the acceleration due to gravity - see your book of constants or refer to the constants which are usually given with a test paper so a = g*3/13 The tension is given by substituting the above in either of the two force equations: T = g*2*m1*m2/(m1 + m2) so T = g*80/13 You should check how these equations are derived here: http://en.wikipedia.org/wiki/Atwood_machine