Need help deriving a formula

  • #1
Omar.Castillo
11
0
Hey could anyone help me out there to know how you get to the formula of free fall displacement. D= 1/2 x g x t^2? I really have no clue of how to get it using other formulas. I started using the D=Vi x T + 1/2 x A x T^2 but then I got stuck I didnt know which other formula to bring into cancel the variables I NEED HELP PLEASE :D
 

Answers and Replies

  • #2
Doc Al
Mentor
45,450
1,911
If you know the formula for uniformly accelerated motion ([itex]D = v_i t + 1/2 a t^2[/itex]), then you can get the formula you need by setting the initial speed to zero and the acceleration to g. That gives you [itex]D = 1/2 g t^2[/itex].
 
  • #3
dextercioby
Science Advisor
Homework Helper
Insights Author
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It's also important to make the wise choice of the sense of the coordinate axis along the displacement. That is, assuming the [itex] \vec{g} [/itex] field is pointing downwards, choose the vertical axis with the same sense.

Daniel.
 
  • #4
Dr.Brain
538
2
There is no formula here . As Doc Al put it, the initial velocity has to be set to zero for the formula to be applicable , so the formula seems to be forced.It is better to get hold of the three basic kinematic equations rather than learning formulae for each and every situation.

BJ
 
  • #5
wisredz
111
0
Try to draw the velocity-time graph. The area under the curve will give you the displacement.
 
  • #6
Omar.Castillo
11
0
Thanks

Hey thanks to all you guys

I never did know you could set the initial velocity to zero! that solved the entire problem thank you. Now I am wondering why I never thought of that well anyways thanks guys
 
  • #7
punjabi_monster
60
0
yes initial velocity can be set to zero if the object stops of an instant, or if it starts from rest.
 

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