# Homework Help: Projectile motion gun help

1. Feb 9, 2012

### andrewi7

1. The problem statement, all variables and given/known data

7. During World War I, the German army bombarded Paris
with a huge gun referred to, by the Allied Forces, as “Big
Bertha.” Assume that Big Bertha fired shells with an initial
velocity of 1.1 x 10^3 m/s [45° above the horizontal].

(a) How long was each shell airborne, if the launch point was the same as the landing point

2. Relevant equations

dy = v1xT+1/2ax X t^2

3. The attempt at a solution

v1 = 1.1 x 10^3
a= -9.81
t = ?

2. Feb 9, 2012

### xlava

I assume "by the same point as the landing point" means the same y coordinate. If the point was the same the gun would be firing straight up.

Anyway, since the gun is at a 45 degree angle, you can find the y component of the initial velocity, and you know the acceleration of gravity. Just use the equation x = x0 + v0t + .5at^2 to solve for t.

3. Feb 9, 2012

### andrewi7

What would x equal

t = Squared root x-.5(-9.81)