Physics.
posted by Lissa. .
A 500 g block lies on a horizontal tabletop. The coefficient of kinetic friction between the block and the surface is 0.25. The block is connected by a massless string to the second block with a mass of 300 g. The string passes over a light frictionless pulley as shown above. The system is released from rest.

Start with a freebody diagram (FBD).
It solves most statics problems automatically when you isolate the system into individual pieces.
Start with the 500g block, mass m1.
Normal force=m1g
coefficient of friction, μ_{k}=0.25
Frictional force = μ_{k}m1g
Let tension in string, T
Acceleration, a = (Tμ_{k}mg)/m
=T/m1μ_{k}g)
For the block at the other end of the string.
Net vertical force
=m2gT
Acceleration, a
=(m2gT)/m2
=gT/m2
Since two accelerations must be equal, we have
T/m1μ_{k}g) = gT/m2
Solve for t and substitute into formulas above to get a, acceleration.
m1=0.500 kg
m2=0.300 kg
μ_{k}=0.25
You should get acceleration, a=2.1 m/s² approximately. 
2.14