- #1
SteelDirigibl
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Homework Statement
I just had my physics final... doing this from memory, so if you think I have left something out let me know.
Basically we have a setup like the attached diagram. frictionless surface up top, masses of the hanging block is 5 kg, and the other block is 3 kg. acceleration of this system is 4.0 m/s2
I realize I forgot to label the tensions, but I was to find the tension of the string "above" (before) the pulley, as well as the tension of the string from which M2 is hanging. Let's call these tensions T1 and T2 respectively.
I was then to find the torque on the wheel.
The last thing I was to do is find the value for the ratio I/R2 where R is the radius, and I assumed I was meant to be inertia. I assume this would give mass of the pulley?
Homework Equations
I=mR2
F=ma
[tex]\tau[/tex]=I[tex]\alpha[/tex]
The Attempt at a Solution
First, to find tension in T1 (the top part of string) I simply did F=ma, or 3*4=12N
For the second tension, I did F=mg-ma, or 9.8*5-4*5, 5*(9.8-4)=29N
I'm fairly sure of these parts. So for the torque on the pulley, it would just be the difference in these two tensions, 17N?
From there, we have the torque equation, and say 17N=I*4
hmm now that I wrote that down it seems wrong. And I seem to recall simply doing 17/4 and saying that was I/R, or 4.25 kg. which I feel is wrong... so... now what? if for only the sake of knowing why I was wrong...