# Contact Forces with a Massless String

1. Oct 7, 2008

### Inertialforce

1. The problem statement, all variables and given/known data
Three blocks of equal mass (m = 0.88kg) are placed in a row onto a rough ramp (μ=0.77) whose angle of inclination is 35 (degrees). Each block is connected to the other by a massless string. Suppose you pull upwards on the top block with a force of 34.9N. Answer the following:

a)Calculate the acceleration of the system.

2. Relevant equations
ΣFx

3. The attempt at a solution
I have already drawn a free body diagram, co-ordinate plane, and vector diagrams for each of the 3 masses. I also realize that the acceleration of the system holds true for any one of the blocks, that is to say acceleration at m1 equals to acceleration at m2. Furthermore I also realize that all 3 masses are of equal mass.

My problem in trying to figure out the acceleration of the system in this case, would be isolating the acceleration ("a"), because there are a lot of tensions to take into account in this question.

2. Oct 7, 2008

### Hootenanny

Staff Emeritus
Sounds like your on the right track. The next step would be to write down Newton's second law for each individual block, so that you end up with a system of three linear equations.

3. Oct 22, 2008

### Inertialforce

I found the acceleration (a= 32.2m/s (squared)) for the question but when I got it handed back to me, it said to double check my free body diagrams because there was a mistake in it. This obviously would then make my acceleration calculation incorrect. I have tried to redo my free body diagrams already but would it be possible for someone to post what they would have gotten for the free body diagram(s) so that I could compare diagrams so as to understand this question better?

4. Oct 23, 2008

### Hootenanny

Staff Emeritus
Perhaps it would be better if you posted your FBD's are we could point out where you have gone wrong.