What is the mass of the bottom weight in this pulley system?

[bignasty]

The system is a 3kg weight on a table top attached to a string leading to a pulley at the end of the table. Attached to the string straight down is a weight with an unknown mass:


( )--------------- 3kg
l
l
l
l
? kg

Question:
The system shown is released from rest and moves 81.6 cm in 2.55779 seconds. The acceleration of gravity is 9.8m/s^2. What it the mass in kg of the bottom weight. All surfaces are frictionless.

Please, if someone could explain the process to me, or perhaps even provide the correct answer so I can work backwards, it would be greatly appreciated, or perhaps even

 

[MathStudent]

any ideas??
heres a hint: The force of tension on the 3kg weight equals the force of tension on the unknown mass.
Use kinematics equations to find the accleration of the 3kg weight, then use Newton's 2nd law to find the force of tension.

Both boxes will have the same magnitude of acceleration.

 

[bignasty]

Thanks

Thanks for the tip, I finally got it!