# Homework Help: Projectile Question

1. Oct 1, 2007

### jbutl3r25

During World War I, the Germans had a gun called Big Bertha that was used to shell Paris. The shell had an initial speed of 1.11 km/s at an initial inclination of 35.8 degrees to the horizontal.
a.How far away did the shell hit? Answer in km.
b. How long was it in the air?

I have a RECTPOLAR program on my calculator that we are allowed to use. I know I need the resultant and the angle for that to give me the x magnitude and the y magnitude. How would I go about setting this up?

2. Oct 1, 2007

### Mentz114

Try

Vx = V.cos(35.8) horizontal component

Vy = V.sin(35.8) vertical component

3. Oct 1, 2007

### jbutl3r25

i don't think that makes sense...

4. Oct 1, 2007

### jbutl3r25

cos(35.8) gives me -.32 and sin(35.8) gives me -.95

i dont think that works

5. Oct 1, 2007

### Mentz114

Make sure you have your calc. set to degrees ( as opposed to radians).
Cos(35.8) = 0.81106.

6. Oct 1, 2007

### jbutl3r25

ohh ok now i got that...

so vx = .811 and vy = .585

so should i go and do the vf, vo, a, d, t set up?
like
vx .811
dx?
t

vfY
voY 0
aY -9.8
dY
t

and if so, how would i find a 3rd component to the Y part?

7. Oct 1, 2007

### Mentz114

Not quite. Look at post #2 again.

Vx = 1.11*0.811 Km/s
Vy = 1.11*0.585 km/s

Using Vy you can work out how long the shell is in the air ( think of a stone thrown vertically with Vy ). The time taken to get to where Vy=0 is half the travel time. When you know the travel time, multiply by Vx to get the distance.

Last edited: Oct 1, 2007