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After Class Practice Set 1 Question 33
Mariana_6094
#1 Posted : Friday, May 21, 2021 7:57:50 PM
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Hi, I had a question about question 33 on AC set #1: it asks what the torque will be exerted on the second hand, but I am just confused as to why they used the massed for the minute hand for the second hand and why they used 3/2 as the length of the second hand. Thank you!
INSTR_Katrina_128
#2 Posted : Friday, May 21, 2021 11:41:52 PM
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Hi Mariana!

I've asked Head Office to change the wording. I think that the "minute / second" hand wording is a typo! Thank you for asking about this.

Here is an image that illustrates what's going on here: https://i.ibb.co/gSQ6GM6/Capture.png

Remember that the mass of the minute hand will act at its center of mass, which we assume is at the MIDDLE of the bar, which is at 1.5 m (or 3/2 m).

So, the sum of the torques is:

total torque = torque of applied force + torque of weight = (5 N)(3 m) + (100 N)(1.5 m) = 15 Nm + 150 Nm = 165 Nm

Let me know if this helps! 😊
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