(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

In the figure below, the incline is frictionless and the string passes through the centre of mass of each block. The pulley has moment of inertia I and radius R.

a) Find the net torque acting on the system (the two masses, string and pulley) about the centre of the pulley

b) Write an expression for the total angular momentum of the system about the center of the pulley when the masses are moving with a speed v

c) Find the acceleration of the masses from your results for a and b by setting the net torque equal to the rate of change of the angular momentum of the system

2. Relevant equations

torque = r x F

angular momentum = r x p or Iw

3. The attempt at a solution

a)I got an answer for this but I dunno if its right

F on m2 in direction parallel to incline = m2 x g sin theta

F on m1 = m1 x g

So torque about centre of pulley due to force on m2 is R x m2 x g sin theta, out of the page

and torque about centre of pulley due to force on m1 is R x m x g, into the page

Net torque is (R x m2 x g sin theta) - (R x m x g), out of the page

b) I'm not sure how to do this. Do I calculate the angular momentum of each of the masses about the centre of the pulley and add it with the angular momentum of the pulley? But if this is the case, I don't know what the angular velocity of the pulley is :S

Angular momentum of m1 about centre = R x m1 v, into the page

Angular momentum of m2 about centre = R x m2 v, into the page

Angular momentum of pulley about it's centre = Iw = 0.5MR^2 w but we don't know w

c)No idea. Do I just set the answer for a to be equal to the differential of the answer to b???

Once again, any help would be much appreciated :)

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# Homework Help: Find the net torque acting on the system

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