# Disk on a plank - HELP!

1. Jan 23, 2009

### sjewenp

disk on a plank -- HELP!

1. The problem statement, all variables and given/known data

a disk of mass M is sitting on a plank of length l and mass m. a constant force F is pulling the plank to the right. assuming no slipping what are the accelerations? how far to the right will the coin move before reaching the left end of the plank?

2. Relevant equations

Idisk=(1/2)MR^2
a=(alpha)R (no slipping parameter)
(tau)=I(alpha) (torque)
F=ma

3. The attempt at a solution

i am not really sure how to set this up. i haven't even tried the second part yet, so unless someone is really giving, i don't expect help with it. anyway, i tried treating the system as just the disk, because the plank is (presumably) sitting on the ground. i set torque = RF-Rf (force pulling and friction force) and F-f=M*a. i solved this system of equations and got nonsense. apparently i'm missing something really fundamental here. sorry i don't have any pics. i hope the description is enough.

Last edited: Jan 23, 2009
2. Jan 23, 2009

### minger

Re: disk on a plank -- HELP!

I have NO idea what your trying to say.
huh?

3. Jan 23, 2009

### sjewenp

Re: disk on a plank -- HELP!

as the plank is pulled, the coin rolls to the left, but the whole assembly is moving to the right. as the question is phrased, it wants to know how far to the right will the coin have moved when it falls off the plank.