# Where does this kinematics equation come from?

1. Jan 29, 2010

### mybrohshi5

g(t)/vox=tan(theta)

g= acceleration due to gravity (9.8m/s^2)
t= time
vox = initial velocity in the x direction

Where does this equation come from?? someone told me to use this to help me solve one of my hw problems and it worked but i have never seen it before and am having a hard time to figure out where the components of the equation actually come from?

could anyone help explain this equation to me?

thank you

2. Jan 29, 2010

### Staff: Mentor

This looks like a formula for calculating the angle below the horizontal that a projectile will be moving after time t after being released with a purely horizontal speed of V0x. It's just tanθ = Vy/Vx. Vy = at = gt.

3. Jan 29, 2010

### tiny-tim

Hi mybrohshi5!

(have a theta: θ and try using the X2 tag just above the Reply box )

If at time t, the angle is θ and the speed is v, then

vsinθ = gt

vcosθ = vx0,

so tanθ = gt/vx0

4. Jan 29, 2010

### mybrohshi5

thank you both! that makes complete sense now.