1. Tardigrade
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  3. Physics
  4. A passenger train is moving at 5 textm texts-1. An express train is travelling at 30 textm texts-1, on the same track and rear side of the passenger tsrain at some distance. The driver in express train applied brakes to avoid collision. If the retardation due to brakes is 4 textm texts-2, the time in which the accident is avoided after the application of brakes is :

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Q. A passenger train is moving at $ 5\,\text{m}{{\text{s}}^{-1}}. $ An express train is travelling at $ 30\,\text{m}{{\text{s}}^{-1}}, $ on the same track and rear side of the passenger tsrain at some distance. The driver in express train applied brakes to avoid collision. If the retardation due to brakes is $ 4\,\text{m}{{\text{s}}^{-2}}, $ the time in which the accident is avoided after the application of brakes is :

WBJEEWBJEE 2006

Solution:

Initial relative velocity of the express trainw.r.t. the passenger train, $ {{u}_{ep}}={{u}_{e}}-{{u}_{p}}=30-5=25m{{s}^{-1}} $ Final relative velocity of the express train w.r.t.the passenger train, $ {{v}_{ep}}=0 $ (because express train comes to rest) From first equation of motion $ {{v}_{ep}}={{u}_{ep}}-at $ or $ 0=25-4t $ or $ 4t=25 $ or $ t=6.25\,s $