1. Tardigrade
  2. Question
  3. Physics
  4. On a long horizontally moving belt, a child runs to and fro with a speed 9 km h-1 (with respect to the belt) between his father and mother located 50 m apart on the moving belt. The belt moves with a speed of 4 km h-1 . For an observer on a stationary platform, the speed of the child running in the direction of motion of the belt is

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Q. On a long horizontally moving belt, a child runs to and fro with a speed $ 9 \,km\, h^{-1} $ (with respect to the belt) between his father and mother located $ 50 \,m $ apart on the moving belt. The belt moves with a speed of $ 4 \,km\,h^{-1} $ . For an observer on a stationary platform, the speed of the child running in the direction of motion of the belt is

Motion in a Straight Line

Solution:

Figure shows conditions of the question.
image
In this case,
Speed of belt w.r.t. ground
$ \therefore v_{BG}=4\,km\,h^{-1} $
Speed of child w.r.t. belt
$ \therefore v_{CB}=9\,km\,h^{-1} $
$ \therefore $ For an observer on a stationary platform, speed of child running in the direction of motion of the belt is
$ v_{CG}=v_{CB}+v_{BG}=9\,km\,h^{-1}+4\,km\,h^{-1} $
$ =13\,km\,h^{-1} $