How Do You Calculate the Coefficient of Kinetic Friction in a Pulley System?

[oldflandark]

Homework Statement

2 objects with mass m1=10 and m2=5 are connected by a light string that passes over a frictionless pulley, they are set up so that m1 is sitting on the desk and m2 is attached to a pulley, is over he desk. if when the system starts from rest, m2 falls 1 meter in 1.2seconds, determine the coeeficiant of kinectic friction between m1 and the desk.

force Friction = Force normal * cooeficiant of kinetic friction

change in x= v-initial*time + .5(accelration)(time^2)



ok so i first found out what the acceleration would be of m2 under those conidtions, found out the force of it then, and then i found the force for if the accelration of m2 was just 9.8m/s^2, and found the difference between that and the first force, and then set that difference equal to Force normal * cooeficiant of kinetic friction, but i still get the wrong answer for kinetic friction cooeficiant.

 

[p21bass]

Did you draw a proper FBD? What did you get for acceleration? And why did you try to find F when a = 9.8m/(s^2)? If you draw a set of FBDs for each part (and one for the whole), all you really need to do is find the acceleration of m2 (which will be the same for m1), and use it to calculate the tension of the string. Then it should be fairly easy to find the coefficient of kinetic friction, using the first equation in conjunction with Newton's 2nd law.EDIT: Basically, you know (by the title) that it's a Newton Motion Law problem, but you don't seem to have used Newton's Laws of Motion!