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Ok, here's the background: I'm a BASE jumper and usually I jump from stationary objects like bridges, cliffs, etc.

But one jump I would love to do at some point involves exiting from the roof of a moving vehicle and clearing a railing of a yet-to-be-named bridge. Knowing that Newton's law of inertia would be at play, I was hoping someone could help me come up with a way to calculate exactly when I should jump from the vehicle so that I'm at the exact halfway point of the bridge's length 1, 2, and 3 seconds after jumping from the vehicle.

These are all just placeholder values so let's say the vehicle is traveling at 15mph and the bridge it's traveling over is 200ft long. Would a headwind of 8mph change anything? Or a tailwind?

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  • $\begingroup$ are you able to jump from a stationary vehicle and clear the railing successfuly? $\endgroup$
    – jsotola
    Apr 29, 2022 at 0:38
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    $\begingroup$ yeah, clearing the railing isn't the most uncertain part though. I'm hoping to find out when I should jump to be at half the bridge's length for the 1, 2, and 3 seconds increments. $\endgroup$
    – adamcasey
    Apr 29, 2022 at 1:23
  • $\begingroup$ clearing the railing cannot be uncertain at all ... it is pointless to attempt a jump from a moving vehicle if you cannot do the jump from a stationary one $\endgroup$
    – jsotola
    Apr 29, 2022 at 2:54
  • $\begingroup$ look to also approximate drag. that is the force the air would apply to you. $\endgroup$
    – Abel
    May 6, 2022 at 18:10

1 Answer 1

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Your speed along the bridge after the jump is the same as the speed of the vehicle minus air friction, which we can ignore for small spans of the jump.

$$ X_1s =\frac{V_{vehicle*1}}{3600}$$

The range of the jump (so you know if you clear the railing) can be estimated like this, again ignoring air friction. Note this time we talk about the speed of your jumping out of the car!

$$R = V_0 \sqrt{\frac{2h}{g}}$$

  • R = rang
  • V_0 = speed of your jump perpendicular to the motion of the car
  • h = difference between the car roof height and the railing
  • g = 9.8m/s^2

Mind all the units must conform.

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  • $\begingroup$ This is great, thank you!! $\endgroup$
    – adamcasey
    May 3, 2022 at 15:47

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