The diagram showing the forces on the masses is shown below.
The acceleration will be in the direction of the heavier mass.
Net force = Weight of 20kg mass - weight of 13kg mass
Weight = mg
where
m = mass
g = acceleration due to gravity = 9.8m/s^2
Net force = 9.8(20 - 13) = 68.6N
Total mass = 20 + 13 = 33kg
Force = mass x acceleration
acceleration = force/mass = 68.6/33
acceleration = 2.08 m/s^2
For block 1,
Net force = W1 - T1
Force = mass x acceleration
Acceleration of mass 1 = 2.08
net force = 20 x 2.08 = 41.6N
Thus,
41.6 = 9.8 x 20 - T1
41.6 = 196 - T1
T! = 196 - 41.6
T1 = 154.4N
Tension in the string form mass 1 = 154.4 N
For block 2,
Net force = T2 - W2
net force = 13 x 2.08 = 27.04N
Thus,
27.04 = T2 - 13 x 9.8
41.6 = 196 - T1
T! = 196 - 41.6
T1 = 154.4N
Tension in the string form mass 1 = 154.4 N