In: Physics
Starting with
"m1g - T1 = m1a ", "T2 - m2g = m2a" and "(T1 - T2) R = I ?"
show the derivation steps of
"(m1 - m2)g = (m1 + m2 + I/R^2) a
Consider the Atwood machine shown at the right. It is an example of pure rotational motion; that is, the center of gravity of the pulley does not translate up/down or to the left/right.
The equations of motion for an Atwood machine that has a pulley with rotational inertia are:
For the smaller mass:
net F = ma
T1 - mg = ma
For the larger mass:
net F = ma
Mg - T2 = Ma
For the pulley:
net ? = ICM?
(T2 - T1)r = I?
In this case net torque is calculated by finding the product of (T2 - T1)r where T2 is the tension in the direction of the pulley's rotation (towards the larger mass) and T1 is the tension in the cord on the other side of the pulley. The radius of the pulley is r. Once again, remember that T1 and T2 can only be equal if the pulley is "massless and frictionless."
The equation a = r? will allow you to relate the linear acceleration of the hanging masses with the angular acceleration of the pulley.