Acceleration and net force for masses on a pulley system

[bekbel]

help, please :)

Homework Statement

Two masses are suspended by a string placed over a pulley supported by the ceiling (m1 = 2.20 kg and m2 = 7.70 kg) Consider up to be positive.
What is the acceleration on the 6.20 kg mass? The net force?
What is the acceleration on the 7.70 kg mass? The net force?

Homework Equations

m2g / (m1+m2) (is that the correct one?)

F = MA

The Attempt at a Solution

For the 6.20 kg mass:

7.70(9.81) / (7.70 + 6.20) = 75.537 / 13.9 = 5.43

6.20 * 5.43 = 33.7 N


Am I anywhere close??

 

[Astronuc]

Does the system look like - http://hyperphysics.phy-astr.gsu.edu/hbase/atwd.html ?

 

[bekbel]

YES. wow that is helpful! thank you.

 

[bekbel]

Ok, now my problem is, there is no mention of tension. So how do I solve for the individual net forces if I don't know acceleration or tension?

 

[Astronuc]

Refer to http://hyperphysics.phy-astr.gsu.edu/hbase/atwd.html#c2

The acceleration is numerically the same for the two masses. The tension acts upward for either mass.

One can find T in terms of the lighter mass, and one knows a in terms of the masses and g, the acceleration of gravity.

 

[bekbel]

wonderful. thank you!

 

[bekbel]

After solving, I found the acceleration of both to be 1.06

The individual net forces are 6.57 for the 6.20 mass, and 8.16 for the 7.70 mass. Do you believe this is correct?