# Homework Help: Rotational motion - finding tangential acceleration

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1. Apr 6, 2015

### prettydumbguy

1. The problem
A 6 kg block is released from a height of 5 m on a frictionless track and goes into a half pipe with a radius of 2 m. Determine the tangential and radial components of the acceleration when the block reaches a height of 2 m.

2. Relevant equations
Ac= v^2/r. At = r*angular acceleration. Maybe Vt = angular velocity*r

3. The attempt at a solution
First I set potential energy at 5m = potential energy at 2m and kinetic energy to find the velocity. I got it and then squared it then divided by 2 to get centripetal/radial acceleration. Now here's where I'm stuck.

I have the radius and the tangential velocity and that's it. I know that tangential acceleration = angular acceleration*r but I don't have the angular acceleration. I can find the instantaneous angular velocity, but it's a single number, not a function so I can't take the derivative. I have no clue where to go from here.

2. Apr 6, 2015

### Staff: Mentor

How about considering the forces acting on the block?