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I'm doing a project where I have to calculate the speed of a ball, passing a certain point.

I want to do this with a laser, by taking the time the laser is broken in comparison of the ball it's size.

Someone who can help me with the correct formula?

Ove Ahlman
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Jonasvr
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  • That seems to be a rather unreliable way of measuring speed. If you don't already have extremely fine control of the velocity of the ball, how can you be sure that the center of the ball will travel exactly through your laster beam? If it doesn't, you will measure too short a time (and thus get too high a speed). – hmakholm left over Monica Apr 26 '16 at 07:44
  • Are you assuming that the ball is moving at a constant speed in a straight line, and its center exactly passing through the laser beam? – Vepir Apr 26 '16 at 07:46

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The laser will "draw" a line segment of apparent length $l$ on the bullet, during time $t$.

The exact formula is

$$v_\perp=\frac lt,$$ where $v_\perp$ denotes the component of the average speed perpendicular to the beam.

  • As commented by others, determining $l$ can be problematic. (Apparent means projected on a plane perpendicular to the beam.) –  Apr 26 '16 at 07:50