Calculating Tension and Friction in a Pulley System

[LiFK]

Pulley Tension friction help??

Homework Statement

http://www.flickr.com/photos/72384417@N06/6533043261/ by LiFK1, on Flickr

Mass1 = 0.750 kg
Mass2 = 0.52 kg
Fk=2.1 N
g= 9.8 N

Homework Equations

F=ma
Mass1(gravity)= (Mass1+mass2)Acceleration
T + m2g - fk = (m1 + m2)a

The Attempt at a Solution

Mass1(gravity)= (Mass1+mass2)Acceleration
7.35=(0.750kg+0.52kg)A
5.787 N = A

T + m2g - fk = (m1 + m2)a
T + 0.52kg(9.8)-2.1=1.27(5.78)
T = 4.35 N
rounded up T = 4.4N

Apparently the answer to this is 4.2 N, but i can't seem to get it.
Can someone tell me what I am doing wrong?
thanks in advance.

 

[technician]

You should draw a diagram showing the forces acting on each object.
The weight has 2 forces it's weight = 0.75 x 9.81 and the tension in the string
The cart has 2 forces the tension in the string and friction.
If you look at these 2 situations you should get 2 equations that enable you to calculate the acceleration and the Tension in the string.
Hope this helps.