# Homework Help: D of a projectile

1. Apr 5, 2008

### roam

A projectile is fired over level ground with an initial velocity that has a vertical component of 20 m/s and a horizontal component of 30 m/s. Using g = 10 m/s², find the distance from launching to landing points.

I don't know what formula to use to solve this question. I would appriciate your help.

I start off by finding the magnitude of the resultant vector: √30² + 20², then I don't know what to do next...

Last edited: Apr 5, 2008
2. Apr 5, 2008

### Snazzy

Relate the time, velocity, and distance in the x-direction with the time, distance, velocity, and acceleration in the y direction.

3. Apr 6, 2008

### roam

So this how you do it:
Horizontal velocity multiplied by flight time equals range.

Find the flight time by working out how long it will take for gravity to reduce the initial vertical velocity to zero. This gives you the "time to go up" and this will be equal to the "time to go down".

a=Δv/Δt so if g=-10ms-2 then:
Δt=Δv/g=0-20/-10=2s so total flight time is 4s.

Now just multiply the horizontal velocity by the flight time 30*4=120m