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October 31st, 2017, 09:31 AM  #1 
Member Joined: Oct 2016 From: Sverige Posts: 32 Thanks: 2  Calculate mass along thread (lineintegral) I've tried to solve this 4 times already, what am I doing wrong? 
October 31st, 2017, 09:41 AM  #2 
Senior Member Joined: Sep 2015 From: Southern California, USA Posts: 1,602 Thanks: 816 
You're doing it wrong :P There's no force here to dot with $dr$ You just have to calculate the differential length along the string and multiply it by the density. I.e. $m = \displaystyle \int_0^1 ~(1+t)\left\\dfrac{dr}{dt}\right \~dt$ see if you can chug through the integral. 
October 31st, 2017, 11:44 AM  #3 
Member Joined: Oct 2016 From: Sverige Posts: 32 Thanks: 2 
integral of (1+t)sqrt(9 + 36t + 36t^2) ? **** me this is the second exercise in this subject, doing mega complex integrals is not part of the course. Is there a simpler way? 
October 31st, 2017, 12:03 PM  #4 
Senior Member Joined: Sep 2015 From: Southern California, USA Posts: 1,602 Thanks: 816  

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