1. The problem statement, all variables and given/known data The 3.2kg , 37-cm-diameter disk in the figure is spinning at 350 rpm . How much friction force must the brake apply to the rim to bring the disk to a halt in 2.4s? 2. Relevant equations F = m * a I = (1/2) * mass * radius2 (I probably need to use this but I can't figure out how it works in) rotational speed = rotations/sec * circumference 3. The attempt at a solution I've tried going about it multiple ways, but I think I'm just leading myself in circles Going to try to solve using F = m * a Solving for a: 350 rpm / 60 seconds = 5.83 rotations/second 5.83 rotations / second * (2π * .37m / 2) m/rotation = 6.77 m/s If I want to go from that to 0 m/s in 2.4s then it's (6.77m/s) / 2.4s = 2.82 m/s2 So since F = m * a = 3.2kg * 2.82 m/s2 = 9.03 N Except that answer is wrong. I would love to use the different rotational formulas but I can't figure out what I'm supposed to use and when to switch from radians to meters and such.