Answer :
it is the D . m1- m2 / m1 + m2
let T be the tension in the string and T is same in both sides of the string and on both sides it is directed upwards acting on m1 or m2.
we assume the string is not slipping over the pully. no friction.
The equation of forces on the side of m1 is
m1 g - T = m1 a m1 moves down ward with acceleration a.
the equation of force s on the side of m2 is
T - m2 g = m2 a m2 moves upwards with acceleration a
add both these equations, you answer
let T be the tension in the string and T is same in both sides of the string and on both sides it is directed upwards acting on m1 or m2.
we assume the string is not slipping over the pully. no friction.
The equation of forces on the side of m1 is
m1 g - T = m1 a m1 moves down ward with acceleration a.
the equation of force s on the side of m2 is
T - m2 g = m2 a m2 moves upwards with acceleration a
add both these equations, you answer