Half Flight projectile motion (1 Viewer)

[Maianbarian]

Hey, could someone verify this for me?

If you are looking at half flight projectile motion (eg a ball rolls off a table) you take g to be positive.

i.e deltay=u_yt + 1/2 a_yt² ------------- From the formula sheet

Becomes: deltay=1/2 gt²

as u_y=0

Instead of it becoming: deltay=u_yt - 1/2 gt² ------- the case in full flight projectile motion

Originally I thought that there should be no difference between half and full flight projectile motion but if you use the equation for full flight projectile motion and try to find t you end up with it being imaginary which obviously can't happen.

 

[Xayma]

g has no positive or negative values, the positive or negative refers to the direction and by convention up is positive.

 

[Jase]

in the case of "full flight projectile"

the first half of the projectile is moving in an upwards direction (opposing gravity), until the maximum point. This means that the vertical range (delta y) will also be negative.

- deltaY = blahblahblah.... -1/2 g t*2

i.e ... solving for t will give u a positive real number and probably a negative one which is ommited.

i hope that made some sense ? ^^

 

[untamedanimal]

It doesnt matter whether you use up or down as positive as long as you are consistent. You cant take gravity as a positive value and then do a ball falling down off a table as negative. It will only be negative if you take acceleration as negative

 

[Maianbarian]

Ahh ok I get it now, with my half flight projectile motion the only vertical displacement is down so if I take down as being negative then delta y is also negative. Cheers everyone