projectile motion?

Question

I would like a refresher in the basics of projectile motion for algebraic physics. I know theta and the initial velocity. I need to find the max hight reached and the disstance it travils before hiting the ground. I would like some help with just remebering the equations needed for projectile motion. Thanks.

Answer 1

Assuming you start with an initial velocity (v) and an angle (theta), your first step is to break the velocity into horizontal (vx) and vertical components (vy).

vx = v cos theta
vy = v sin theta

To find the range on level ground, assume that the downward velocity will be the negative of the upward velocity and use the following equation to find the time in the air. a is the acceleration due to gravity (-9.8 m/s2)

vf = vi + at

-vy = vy + at

-vy - vy = at
-2(vy)/a = t

The negative cancels out because a = -9.8 m/s2

Take the time in the air and multiply it by the initial horizontal velocity (vx) to find how far it goes.

d = (vx)t

To get the height, use exactly half the time you found above, then plug that into the following equation:

height = 1/2 (vy) t


If you want to work the problem in feet, use a = -32.2 ft/s2 instead.