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Projectile Question

  1. Oct 1, 2007 #1
    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. jcsd
  3. Oct 1, 2007 #2

    Mentz114

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    Gold Member

    Try

    Vx = V.cos(35.8) horizontal component

    Vy = V.sin(35.8) vertical component
     
  4. Oct 1, 2007 #3
    i don't think that makes sense...
     
  5. Oct 1, 2007 #4
    cos(35.8) gives me -.32 and sin(35.8) gives me -.95

    i dont think that works
     
  6. Oct 1, 2007 #5

    Mentz114

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    Gold Member

    Make sure you have your calc. set to degrees ( as opposed to radians).
    Cos(35.8) = 0.81106.
     
  7. Oct 1, 2007 #6
    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?
     
  8. Oct 1, 2007 #7

    Mentz114

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    Gold Member

    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
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