InterviewSolution
Saved Bookmarks
InterviewSolution
| 1. |
A train normally travels at a uniform speed of `72 km//h` on a long stretch of straight level track. On a particular day, the train was forced to make a `2.0` minute stop at a station along this track. If the train decelerates at a uniform rate of `1.0 m//s^2` and accelerates at a rate of `0.50 m//s^2`, how much time is lost in stopping at the station ?A. 2 minB. 2 min 30 sC. 30 sD. 2 min 20 s |
|
Answer» Correct Answer - B Case-I : Actual time spend in decelerating =`(v - u)/(a) = (0 - 20)/(-1.0) = 20 s` Distance travelled in decelerating =`20 xx 20 - (1)/(2) xx 1 xx 20^2 = 400 - 200 = 200 m` Time that train will have taken if it had travelled uniformly with `20 m//s` for `200 m = (200)/(20) = 10 s` Extra time spend in decelerating `= 20 - 10 = 10 s` Case-II : Actual time spend in accelerating =`(v - u)/(a) = (20 - 0)/(0.5) = 40 s` Distance travelled in these `40 s` =`0 xx 40 + (1)/(2) xx 0.5 xx 40^2 = 400 m` Time that the train will have taken if travelled uniformly with `20 m//s = (400)/(20) = 20 s` Extra time lost due to acceleration `= 40 - 20 = 20 s` Total extra time `= 10 s + 2 min + 30 s = 2 min 30 s`. |
|