A car placed on incline and a mass placed on the car

[eren.kizildag]

Homework Statement

The car of mass M is sliding on the incline. A mass of m is placed as shown. There is friction between m and M in the vertical surface of M . The incline is frictionless. System is released, and it is observed that m moves parallel to the incline. We are asked to find the kinetic coefficient of friction. (Angle is theta)

Homework Equations

Ff+masin(theta)=mg, N=macos(theta), Ff=Mk*N where Mk is the kinetic coefficient of friction. N is the reaction force between M and m.

The Attempt at a Solution

I have chosen the ordinary coordinate system. The masses must have same acceleration. (In both x and y direction). I also showed the friction force acting on m. And I wrote down reaction forces, but could not get the correct answer.

(I'm sorry, I am new at the forum, and I don't know how to use the forum properly. If I made a mistake about the body of the message, please forgive me.)

 

[gneill]

Hello eren.kizildag. Welcome to Physics Forums.

Since m is not sliding on M, both M and m must be moving downslope together. Have you worked out the downslope acceleration of the pair as a function of g and θ ?

 

[eren.kizildag]

Yeah, but I got nothing.

 

[gneill]

Yeah, but I got nothing.

No acceleration downslope? Perhaps you could show your calculation?