Angular Acceleration/Tension - Need help , please

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The discussion focuses on calculating the angular acceleration and tensions in a pulley system with two masses attached. The system consists of two pulleys with radii of 0.5m and 1.75m, and a combined rotational inertia of 1.5 kg*m². The user initially calculated the torque as 57.58 N*m, leading to an angular acceleration of 38.39 rad/s², but received feedback indicating that the angular momentum of the masses must also be considered. For tension calculations, the forum suggests applying Newton's second law (F = ma) for each mass.

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1. Homework Statement
Two pulley wheels, one of radius 0.5m and the
other of radius 1.75 m, are mounted rigidly on
a common axle. The rotational inertia of the
two pulleys, which are clamped together, is
1.5 kg*m2. A mass of 7.5 kg mass is attached
on the left and a mass of 5.5 kg mass on the
right, as shown.

Here is the image: http://yfrog.com/jwpulleyp

a.) Find the angular acceleration of the system. Take clockwise direction to be positive. Units in rad/s^2

b.) Find the tension in the cord attached to the 7.5 kg mass (units in N)

c.) Find the tension in the cord attached to the 5.5 kg mass (units in N)

2. Homework Equations

net torque = I * a

3. The Attempt at a Solution

Torque = I * a
Torque = m2*g*r2 - m1*g*r1
torque = 5.5*9.8*1.75 - 7.5*9.8*.5
= 57.58

a = Torque / I
=> 57.58 / 1.5 =38.39 rad/s2

Tried to submit the answer, but it was wrong. Don't know what I am doing wrong in part A. And I'm not sure how to do attempt Part b or c. Any advice appreciated!
 
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hi jaredsees! welcome to pf! :smile:

(try using the X2 icon just above the Reply box :wink:)
jaredsees said:
a = Torque / I
=> 57.58 / 1.5 =38.39 rad/s2

erm :redface: … don't the two masses have angular momentum also? :wink:

(and for the tension, use F = ma for each mass)
 

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