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Homework Help: Projectile motion

  1. Sep 12, 2010 #1
    1. The problem statement, all variables and given/known data

    A cargo plane is flying horizontally at an altitude of 11.5 km with a speed of 860 km/h when a large crate falls out of the rear loading ramp. (Ignore any effects due to air resistance.)

    (a) How long does it take the crate to hit the ground?

    2. Relevant equations

    y=y+v(sub y)(t)+1/2a(sub y)(t)^2

    v(sub y)=v(initial)(sin58)

    3. The attempt at a solution

    I attempted these equations but since the initial speed of the crate is the same as the plane and there is no angle, I cannot find the y value of velocity, in order to find the time it took to hit the ground.
  2. jcsd
  3. Sep 12, 2010 #2


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    That statement is correct, but I'm not sure what you mean about there being no angle.

    Think about this: how fast is the plane moving vertically? In other words, what is the rate of change of the plane's height? As you said yourself, once you figure that out, the initial vertical speed of the crate will be the same.
  4. Sep 13, 2010 #3


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    When a large crate falls out of the rear loading ramp,

    vx = 860 km/h =238.9 m/s

    vy = 0

    y = 11.5 km = 11500 m.

    Use the kinematic equation to find time.
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