Torque and Inertia of objects on Inclined plane

[cooltee13]

Homework Statement

a block with mass m1= 2 kg, and a block of mass m2 = 6kg are connected by a massless string over a pulley in the shape of a solid disk having radius R = .25m and mass M = 10 kg. These blocks are allowed to move on a fixed wedge of angle pheta = 30 degrees. the coefficient of kinetic friction is .36 for both blocks and pulley. Determine A) the acceleration of the two blocks and B) the tensions in the string on both sides of the pulley.

Homework Equations

well, I already solved part A) I just need help with part B. I used the sumTorque = Ialpha, where alpha = a/R. along with this equation below:

The Attempt at a Solution

well, i wanted to solve for a so i did the following:(note f=coefficient of friction*): -T1Rf+60cos(T2)Rf = 1/2mR^2*(a/R) ====> -T1f +60cos(T2)f = 1/2ma.

M2gf - T1f + 60cosT2f = 1/2Ma
M2gf = M1af + 60cosM2af + 1/2Ma
M2gf = a(M1f + 60cosM2f + 1/2M)
a = M2gf/(M1f + 60cosM2f + 1/2M) = .31 m/s^2

Im not sure how to solve for the Tension though, do i use the same equation??

 

[cooltee13]

The answer for B is 7.67 N and 9.22 N.

But I want to know how they got that. Can anybody help please?

 

[cooltee13]

can anybody help? do I need to explain more?

 

[Doc Al]

A diagram would be helpful. Are both sides of the wedge at an angle of 30 degrees with the horizontal?

In any case, assuming you've correctly found the acceleration, just apply Newton's 2nd law to each block separately to find the tensions.

 

[cooltee13]

Im not sure how to put a diagram on this forum, but If i apply Newtons second law, I don't end up with the same Tensions as the book answer.

F = ma
I come up with 6.08 N for T1

 

[Doc Al]

Show exactly what you did to get the tension. (Until I understand the setup better, I cannot verify your answer for the acceleration.)

 

[cooltee13]

how do I insert an image so i can show you the picture?

 

[Doc Al]

One of the icons in the post editing window is for inserting images. Or you can attach a file.