Forces on a rotating drum

1. Feb 27, 2009

robbinz

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

Q
A load of mass 8 tonne is to be raised with a uniform acceleration of 1.1 m/s^2 by means of a light cable passing over a hoist drum of 2 m diameter. The drum has a mass of 1 tonne an a radius of gyration of 750 mm. Find the torque required at the drum if friction is neglected.

A
(87.8 KN-M)

2. Relevant equations

T=Ia = MK^2a ( The a is ment to be alpha )

F=MA

3. The attempt at a solution

Ok so my attempt at the solution was T = Ia(alpha) + F x R ( Taking F=MA )
But it comes out wayyyy wrong.

So obiously I know the solution as I have given it. But I am confused as how to do the working. Can anyone help ?

p.s. First forum post....yayyy :D

Thanks

2. Feb 27, 2009

Dr.D

You need a couple of free body diagrams to start things off. Then write the equations of motion for each mass (the drum, the block being raised) and write the relevant kinematic relations. Then it should all fall into place for you.