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PeacefulPumpkin8091

Why can't I use this formula to solve for time? The final velocity isn't 0? Wouldn't a bullet have to come to a stop when going up and down as well? Position isn't given so I figured that motion equation wasn't relevant for the question. This is regarding question 6. Chapter 2 UARM.

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Émilie

Bonjour PeacefulPumpkin8091,

Thank you for using our services! In this week of school perseverance, I would like to congratulate you for your efforts at school, it is not always easy, but your perseverance makes all the difference 🎉💫. Keep up the good work!

I would tend to say that the formula you used is not appropriate for this problem, because we are not certain that the final speed is really 0. Indeed, in your statement, you are given the initial speed (400m/s) and you can assume the acceleration since the bullet is subject to gravity. You also know the movement of your bullet (0m). In this case, you must therefore use a formula which involves these three variables. This is why the following formula was used :

delta x = (vi x delta t) + (1/2 x a x delta t^2)

Here is a sheet that might help you:

https://www.alloprof.qc.ca/fr/eleves/bv/physique/les-equations-du-mrua-p1010

I hope I answered your question. Don’t hesitate to write to us again if any questions persist!