Angular Momentum and Average Torque

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SUMMARY

Angular momentum is conserved, meaning the initial angular momentum of 7.87 must equal the final angular momentum. However, the average torque calculation is incorrect; it should account for the change in angular momentum over time. Given that the angular velocity of the rod changes from 0 to 26.03 rad/s in 7 seconds, the average torque is not zero, as the change in angular momentum is not zero.

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mohabitar
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Refer to number 6. This is the one I'm stuck on. So angular momentum is conserved right, so initial angular momentum is equal to final angular momentum. Initial is 7.87 so final must be 7.87, right? And so average torque is just change in angular momentum / change in time, so 0/7=0. What am I doing wrong?
 
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hi mohabitar! :smile:
mohabitar said:
… So angular momentum is conserved right, so initial angular momentum is equal to final angular momentum. Initial is 7.87 so final must be 7.87, right? And so average torque is just change in angular momentum / change in time, so 0/7=0.

no, total angular momentum is conserved, but the angular momentum of the rod isn't …

the angular velocity of the rod changes from 0 to 26.03 in 7 s …

so use one of the standard constant acceleration equations to find the (average) angular acceleration :wink:
 

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