more physics.....please help?

Question

A 7.50 kg block is resting on a horizontal surface, and is connected to a 5.50 kg mass suspended from a string passed over a frictionless pulley.
Find the acceleration of the system and the tension in the string if the surface is:
(a)
smooth, and
(b)
the coefficient of friction is 0.190

Answer 1

a) the weight of the 5.5 kg mass is the force trying to accelerate the system. F= W = m2*g and F = (m1+m2)*a where m2 is the hanging mass.

b) see my answer in your previous question.

Answer 2

http://en.wikipedia.org/wiki/Coefficient_of_friction