# physics

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consider 2 inertial reference frames, A and B, where B (a train) is moving with constant velocity, 10kn/h, in the positive x direction with respect to A.(a person standing on the station platform). if another person is throwing a ball on the train (ie in frame B at a speed of 10m/s in the negative y-direction in the train (ie frame B ), what is the measured velocity of the ball and direction in frame A (ie with respect to the platform xy)?

• physics -

The ball has a downward velocity component if 10 m/s in both reference frames. In addition to that, it has a velocity component + 10m/s in the station platform frame (A).

So, take the vector sum of 10 m/s horizontal and -10 km/h vertical velocity components

• physics -

why is it -10 km/h for the vertical velocity components?because i thought the train is travelling horizontally at 10km/h so it should be a horizaontal component?

• physics -

<<why is it -10 km/h for the vertical velocity components? >>

Because the ball is thrown down. The horizontal relative motion of the two reference frames does not affect vertical velocity componnts when the transformation is performed.

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