Relative Motion



  • 0_1568281841188_15682818006786574739886632777256.jpg

    Question 1



  • @evelye

    Men are running along a road at 15 km/h behind one another at equal intervals of 20m.Cyclists  riding in the same direction at 25 km/h at equal intervals of 30 m. At what speed in km/hr an observer  travel along the road in opposite direction so that whenever he meets a runner he also meets a cyclist

    Speed of Runner = 15 km/hr = 15 * 1000/3600 = 25/6 m/s

    Speed of cyclist = 25 km/hr = 25 * 1000/3600 = 125/18 m/s

    Distance Covered by Observer = x m

    Then Distance Covered by Runner & Cyclist  = 20 -x  & 30 - x

    Time taken by cyclist & Runner is same

    ( 20 -x)/(25/6)  = ( 30 -x)/(125/18)

    => 5 (20-x) = 3 (30 -x)

    => 100 - 5x = 90 - 3x

    => 2x = 10

    => x = 5

    Time taken by runner =  (20 - 5)/(25/6) = 90/25 = 18/5 = 3.6 sec

    Speed of Observer = 5 / (18/5) = 25/18 m/s

    = (25/18) * 3600/1000 km/hr

    =  5 km/Hr



  • @yash-kapoor
    Thanks


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