Calculate Net Acceleration of Masses: F=ma, t=mg+ma, t=mg-ma

[fcb]

Homework Statement

Two masses of 40kg and 120 are connected by a light inextensible string

Calculate the net acceleration of the system of masses
magnitude and tension of the string

Homework Equations

F=ma
t=mg+ma
t=mg-ma

The Attempt at a Solution

120x9.8 = 1176N
40x9.8 = 392N

1176 - 392 = 784N to the right
784=(40+120) x a

a=4.9BUT then i used the t=mg+ma and put in t = (40x9.8)+(40x4.9)
and the answer then came out to be 588N

where have i gone wrong

one answer saids 784N the other saids 588N.

 

[RTW69]

Do a free body diagram on each mass. Tension is the same. You end up with 2 equations and 2 unknowns. The acceleration of the system is 4.9 m/s^2 and the tension in the string is 588 N. I don't see a problem with your analysis.