Hi, I have a problem which I can't figure out. Let us take a sphere which is rolling purely at a constant velocity vo. Now, if the sphere were to collide inelastically with a wall, with coeff. of restitution = e. Then what is the time after which the sphere starts pure rolling again? Given coeff, friction = μ I went about by considering that after the collision, the particle will have evo velocity, but the same angular velocity ω=vo/r. Now, since the sphere is translating, the angular velocity is in the opp. direction. So the frictional force will cause a torque to change ω. So, if the body was initially moving rightwards, with clockwise ω, it's new velocity will be leftwards, but ω will remain clockwise. So the frictional force must act towards right to apply a counter-clockwise torque. After this, I couldn't figure out which way to go.:uhh: Any help appreciated.!