(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Check out my attachment to get an idea what is happening. What we have is an inclined plane with 2 masses (m1 and m2) which are touching one another and the angle of the incline is 30 degrees.

The coefficient of kinetic friction between m1 and the plane is 0.23 = mu_k1

The coefficient of kinetic friction between m2 and the plane is 0.51 = mu_k2

m1 = 2.5kg

m2 = 3.1kg

theta = 30 degrees

The question is to find the acceleration of the pair of masses, and the second question is find the force of m1 on m2

2. Relevant equations

F=ma

3. The attempt at a solution

I applied Mr Newton on each mass individually to get

for mass m1:

x direction (parallel to the inclined plane):

[tex]-F_{21}-\mu_{k1}N_{1}+m_{1}g\sin(30)=m_{1}a[/tex]

y direction (perpendicular to the inclined plane):

[tex]-m_{1}g\cos(30)+N_{1}=0[/tex]

for mass m2:

x direction:

[tex]F_{12}-\mu_{k2}N_{2}+m_{2}g\sin(30)=m_{2}a[/tex]

y direction:

[tex]-m_{2}g\cos(30)+N_{2}=0[/tex]

I used [tex]F_{12}=-F_{21}[/tex].

I put all that into the mix and out popped a = 9.33m/s^2, which is wrong.

The answer says a = 1.6m/s^2. I am pretty sure my maths is ok. I'd say the problem is in my application of Newton but can't see anything wrong.

Thanks in advance

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# Homework Help: Easy newtons law problem

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