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xth

two dists

xth
Jul 30th, 2019
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  1.  
  2. the time to travel from A->B = 3 hours
  3. Going from B->A has the same distance, but time of 3 and half hours
  4. you travel downhill at 75 mph
  5. over flat terrain at 60 mph
  6. and travel uphill at 50 mph
  7. the road is the same road each way
  8.  
  9.  
  10. So there are two different time functions..?
  11.  
  12. lets use a simple example
  13.  
  14. we have 10 mile walk. i can walk 5mph uphill and 7.5mph downhill.
  15. the walk is totally up or downhill.
  16. it would be 2 hours to walk up the hill
  17. but only 1 hour and 20 minutes down the hill
  18.  
  19. We can probably model the difference between the two equations
  20. Let t1 and t2 represent times to walk uphill or downhill
  21. remember the speed = distance over time
  22. so time = distance over speed
  23. t1 = d/5, t2 = d/7.5
  24.  
  25. if we know what t1 and t2 are, we can find out what d is
  26. and vice versa
  27.  
  28. as distance = time multiplied by speed
  29. d = t1*5 = t2*7.5
  30. replace t1 and t2 with actual numbers
  31. d = 2*5 = 1*7.5 + 1/3*7.5
  32. d = 10 = 10
  33. :)
  34.  
  35.  
  36. now lets tackle the previous fight
  37.  
  38. it takes 3 hours to travel from A to B
  39. but 3 and a half hours to travel back the same road
  40.  
  41. going uphill averages 50 mph
  42. on flat terrain averages 60mph
  43. and going downhill averages 75 mph
  44.  
  45. Let t1 represent A to B, t2 represent B to A
  46. time = distance over speed
  47. There will be 3 different distances, one for each terrain
  48. d1 : uphill, d2 : flat, d3 : downhill
  49. for t2, just flip down and up
  50. 3.0 = d1 / 50 + d2 / 60 + d3 / 75
  51. 3.5 = d1 / 75 + d2 / 60 + d3 / 50
  52.  
  53. we can get d1 by multiplying both sides by its divisor
  54.  
  55. 150.0 = d1 + 50d2/60 + 50d3/75
  56.  
  57. subtract 50d2/60 + 50d3/75 from both sides
  58. d1 = 150.0 - 50d2/60 + 50d3/75
  59. Simplify terms
  60. d1 = 150.0 - 5d2/6 + 2d3/3
  61.  
  62. we can do the same for the second distance
  63. 3.5 = d1 / 75 + d2 / 60 + d3 / 50 maybe?
  64.  
  65. screw that
  66. im just going to start doing distance = time multiplied by speed
  67. let big D represent distance.. its made of smaller distances
  68. D = d1 + d2 + d3
  69. ...
  70. im stuck at how to make the equations
  71. i feel like this should work but idk what to do now
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