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Inclined Force with Pulley

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  1. Nov 30, 2014 #1
    I am having trouble on one of my homework problems. The problem is

    What is the acceleration of the system if M1 is 5 kg and M2 is 4kg and the coefficient of friction between M1 and the table is 0.20? There is an image along with the problem. Basically it is just like a standard inclined plane problem where M1 is the box on the ramp and M2 is the weight being pulled down. The angle of incline is 40degrees.

    The teacher stated that the answer was 0.02m/s2, but that we would have to show all work to recieve credit. I have worked it out several times, but have not been able to get that answer. He taught is to do this by plugging values into the equations T−mg=ma and T−Ff=ma, setting the tensions equal to each other, and finding the acceleration. I did this, but got something along the lines of 3.5m/s2. I looked up alternative methods online, but they didn't seem to use the second equation, and I was a little confused. If someone would teach me the steps to solve this problem, I would very much appreciate it.

    The specific work I did was the following:
    T = mg + ma
    T = 4(9.8)+4(-a)
    T = friction + ma
    T = 0.2(38) + 5a
    Set equations equal to each other.
    39.2 - 4a = 7.6 + 5a
    a = 3.5m/s squared.
     
  2. jcsd
  3. Nov 30, 2014 #2

    haruspex

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    You've not considered all the forces acting down the slope on m1.
     
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