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Messages - Jing_Wang

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Test 2 / Re: TT2-2019 Past Test, Morning Sitting
« on: October 29, 2020, 01:26:28 AM »
I encountered the exact same problem and I think (C2)' should equal -e^t/(e^t+1).
Consequently, the constant c2 I find for part (b) is ln2 instead of -ln2.
Also, if it is intended in the question that g = 12/(e^t+1), most things in the solution are to be multiplied by a factor of 6.

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Chapter 2 / Re: Section 2.2 Question 30 part c and d
« on: September 23, 2020, 08:59:09 AM »
b. y=v·x as given. Use multiplication rule for y' (with respect to dx):
y' = (v·x)' = (v')·x + v·(x') = x·v' + v.
c. The first equation follows immediately from (b). Eqs. (31) is obtained by moving v to the other side.
Hope this helps

3
Chapter 2 / Textbook 2.3 Exercises 21b - Is a Differential Equation necessary?
« on: September 20, 2020, 04:16:58 AM »
Hi, I'm a bit confused about the solution of this question. Assuming w and B are as defined and R = Ee, there isn't really a force that depends on v, so one way to obtain the answer is simply to set the sum of all forces equal to 0 and solve for e. Even if we were to set up a differential equation, the equation would only involve v' and some constants, and the solution is trivial. Is this what is expected in this question?
Any help is appreciated. Thank you!

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