Integral Solve for u + at^2/c^2

  • Context: Undergrad 
  • Thread starter Thread starter jcsd
  • Start date Start date
  • Tags Tags
    Integral
Click For Summary

Discussion Overview

The discussion revolves around solving the integral \(\int^{0}_{\frac{-u}{a}} t\sqrt{1 - \frac{(u + at)^2}{c^2}} dt\). Participants explore substitution methods and the implications of changing limits of integration, focusing on the mathematical reasoning involved in the solution process.

Discussion Character

  • Mathematical reasoning, Technical explanation, Debate/contested

Main Points Raised

  • One participant presents the integral and expresses concern about its complexity.
  • Another participant suggests a substitution \(\frac{u + at}{c} = \cos \theta\) and provides a transformed expression for the integral, indicating that it can be solved independently afterward.
  • A third participant challenges the limits of integration provided in the substitution, asserting that they are incorrect and providing the correct limits based on the values of \(t\).
  • A later reply acknowledges the correction regarding the limits and notes that it simplifies the problem slightly.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the limits of integration, with one participant correcting another's claim. The discussion reflects differing views on the substitution method and its application.

Contextual Notes

Limitations include the dependency on the correctness of the substitution and the interpretation of the limits of integration, which remain unresolved in the discussion.

jcsd
Science Advisor
Gold Member
Messages
2,113
Reaction score
13
Can someone solve this integral as the answer I get looks suspicously complicated:

[tex]\int^{0}_{\frac{-u}{a}} t\sqrt{1 - \frac{(u + at)^2}{c^2}} dt[/tex]
 
Physics news on Phys.org
Make the substitution [itex]\frac{u + at}{c} = \cos \theta[/itex]. You should be able to get it down to this:

[tex]\frac{c}{a^2} \left (u\int _{\frac{\pi}{2}} ^{\arccos \left(\frac{u}{c}\right)} \sin ^2 \theta d\theta - c\int _{\frac{\pi}{2}} ^{\arccos \left(\frac{u}{c}\right)} \sin ^2 \theta \cos \theta d\theta \right )[/tex]

And you can easily solve that on your own.

EDITED to fix limits of integration as per HallsOfIvy's comment.
 
Last edited:
The substitution might work but the limits of integration are wrong. When t= 0, cos[theta]= u/c so [theta]= cos<sup>-1</sup>(u/c). When t= u/c, cos[theta]= 0 so [theta]= [pi]/2.
 
Thanks for that, I realized I made a slight error so it became slightly easier to solve.
 

Similar threads

  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 27 ·
Replies
27
Views
4K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 19 ·
Replies
19
Views
5K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 17 ·
Replies
17
Views
6K
  • · Replies 3 ·
Replies
3
Views
3K