1. The problem statement, all variables and given/known data A particle of mass m starts his motion from rest in the top of a inclined plane. It slides down the plane and enters a circular rail of radius R. (a) What's the minimum value of b for the particle not to Uma partícula de massa m parte do repouso no topo de um plano inclinado, desliza e entra numa calha circular de raio R como mostra a figura. (a) What is the minimum value of b so that the particle does not leave the rail in her movement? (b)Assume that b = R. Determine the force exerted on the particle by the rail when it reaches the height R. 2. Relevant equations Em=K+U Em is mechanic energy, K is kinectic energy and U is gravitic potential energy. 3. The attempt at a solution (a)When the particle starts his motion her mechanic energy is mg(2R+b). When it reaches the top of the circular rail her mechanic energy will be mg(2R)+.5mv2. Since the mechanic energy is a constant: mg(2R+b)=mg(2R)+.5*mv2 Solving the equation I got b=-v2^2/(2*g) I'm not sure if I did it the right way tho. (b) I have no idea how to solve it. I tried working the function I got in (a) and derivating to obtain the accelaration, without success, since the accelaration would be 0. I need some hint to solve it... Thanks.