I feel retarded but I don't see where the edit button is, so I'm just going to write something here. I wanted to make clear that F in the problem is the friction force experienced by the particle. And also, my calculations above are wrong, the spring is stretched by R at the initial position...
Homework Statement
A particle of mass m is moving along a path composed by two two quarters of circumference of radius R (see attached picture). The spring acting on the particle has a known constant equal to k and an equilibrium length equal to R (the radius again). Due to friction, on the...