# Projectile motion - help needed

zebra1707
Projectile motion - urgent help needed

## Homework Statement

Target is projected at an an angle to the horizontal, initial speed 4 m/s, unknown angle and unknown distance to the target. Height of the target is 0.8m.

Need to find the minimum angle.

## Homework Equations

v= u+at
v = delta s/delta t
sin theta ?

## The Attempt at a Solution

0 = 4 + (-9.8)t
9.8t =4/9.8
t = 0.408 (0.41) s (i think that this is wrong as it may be the time for the "entire" flight of the projectile.

v = delta s/delta t
v delta t = delta s
4 x 0.41

Delta s = 1.63

sin-1 = 0.8/1.63

angle = 30 degrees

Can the gurus please check this because I think that I have the entire flight of the projectile - not the max height where it will hit the target.

Cheers and thanks.

lswtech

You should try setting up equations for both vertical and horizontal motions. Then you should have an unknown "d" for distance in the equations. Join x-y by cancelling the parameter "time t". Consider d as a real root and you are done!