# Homework Help: Pulling mass with motor through pulley (with mass)

1. Oct 13, 2013

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

http://puu.sh/4PDPV.png [Broken]

2. Relevant equations

τ = I*α
τ = r*F

3. The attempt at a solution

EDIT2: Nevermind, manipulated the torque equations wrong, got it now

EDIT: Tried again and ended up with an actual answer, but still got it wrong :/
This is the FBD I used http://puu.sh/4PH7l.png [Broken]

m = 1060 kg
Ft2 = 10900
I = 75.5 kg*m^2
r = 0.757 m

1060a = Ft1 - 1060*9.81

τ = I*r*a
τ = r*F
F = 10900 - Ft1

I*r*a = r*F
I*a = F

75.5*a = 10900 - Ft1

1060a = Ft1 - 1060*9.81
Ft1 = 1060a + 1060*9.81

75.5a = 10900 - Ft1
75.5a = 10900 - (1060a + 1060*9.81)
75.5a = 10900 - 1060a - 1060*9.81
1060a + 75.5a = 10900 - 1060*9.81
a = (10900 - 1060*9.81) / (1060 + 75.5)
= 0.44157

Last edited by a moderator: May 6, 2017
2. Oct 13, 2013

### Simon Bridge

You need two free-body diagrams.
You are given the forces on the pulley and the mass
- just sketch out the fdb's and look at what forces are present.