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Ask iit jee aieee pet cbse icse state board community Discussion Response Post to: The ultimate challenge in Mechanics from Feynmann
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feynmann (2236)

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Olaaa!! Perrrfect answer. 404  [512 rates]

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Anyway, I can provide u a solution in cartesian co-ordinates .
 
see, the controlling differential eqns are clearly.........
 
 
dx/dt = u cos ..................... ( 1 )
dy/dt = usin  .......................( 2 )
y/( x - vt) = tan ....................... ( 3 )
 
y = - r sin  .................. ( 4 )
Now the task is to solve these coupled differential eqn .
 
From ( 3 ) we have
 
                  x - vt = y cot
dwrt 't'  
                   dx/dt -v = dy/dt cot - y cosec^2() d/dt
 
combining  ( 1 ) & ( 2 )  with this eqn we have
 
                     u cos   - v = u sin  cos /sin  + r cosec d/dt
 or ,                 d/dt = -v/r sin  .................. ( A )
 
 
differentiating ( 4 ) wrt 't ' , we get
 
                   u sin   = - d/d  ( r sin ) d/dt
 
combining with ( A ) we get
 
               u/v  =  cos   + sin  1/r  dr/d
 
or ,         u/v cosec  - cot  = 1/r dr/d
 
Now integrating it and putting the boundary condition that r= d at = /2
 
we get 
 
             r/d  = ( 1- cos ) ^u/v / ( sin  ) ^ ( u/v + 1 )
 
 
 
 
 
 
 
 
 
 
 this reply: 55 points  (with 11 Olaaa!! Perrrfect answer.   in 11 votes )   [?]
 
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