Identify the correct expression for the magnitude of acceleration a of the system consisting of two masses m1 and m2 (m2>m1) connected by a light string over a frictionless pulley.
a) a=m1+m2m2−m1g
b) a=m2−m1m2+m1g
c) a=m2m2−m1g
d) a=m1m2−m1g