A grindstone in the shape of a solid disk with diameter 0.520m and a mass of 50.0kg is rotating at 800rev/min . You press an ax against the rim with a normal force of 160N, and the grindstone comes to rest in 8.50s .
Find the coefficient of kinetic friction between the ax and the grindstone.
The Attempt at a Solution
The concept of torque has been giving me alot of problems, mostly UNDERSTANDING what the equation means, and when to use them.
So here is how I started out,
850rev/min= 85pi rad/3s
So my logic is I have the inertia, and I have enough information to solve for acceleration which means I can find the torque.
I solve for the acceleration
Here is where I get a bit confused, where I was going with this problem is I was going to solve for the torque using Ʃτz= Iαz
Then when I aquired the torque I was going to use
to find the coefficient of friction.
The solution manual sets Ʃτz= μkNR=Iαz, and solves for μk.
How do we know when to stay at Ʃτz=Iaz or when we have to switch over to ƩFext=Macm?