- #1
dismalice
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Homework Statement
A tradesman sharpens a knife by pushing it against the rim of a grindstone. The 35 cm diameter stone is spinning at 200 rpm and has a mass of 15 kg. The coefficient of kinetic friction between the knife and the stone is 0.20.
If the stone loses 10% of its speed in 10 s of grinding, what is the force with which the man presses the knife against the stone?
Homework Equations
SIgma F=ma
F=mu_k*N
A_c= (Mv^2/r)
I would assume that because the knife is pushed into the stone force should be counted as centripetal force.
The question asked for N for units and values
The Attempt at a Solution
200 rpm * 2pi/60s = 20.944 rad/s
V = 20.944*.175 = 3.6652 m/s
N= 9.8*15= 147N
Velocity With Speed Decay = 3.2987 m/s
F=147*.2= 29.4N
I can't think of anywhere to go from here, and any sort of help would be appreciated.