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Homework Help: Projectile Motion Question

  1. Nov 3, 2009 #1
    1. The problem statement, all variables and given/known data
    A blue car carrying a pizza sign goes over a hill and sees a red car stopped at the bottom. The blue car is unable to stop in time and hits the red car, sending the pizza sign flying.

    The blue car's reaction time is 2/3 of a second.
    The length of the skid marks from the point which the blue car started braking to the point where it hit the red car is 60m.
    The sign traveled 11m before hitting the ground.
    The coefficient of friction between the blue car's tires and the ground is .75.
    The height of the car is 1.47m.
    The angle of the hill is 2 degrees.
    Find the car's initial speed.

    (Assume that the cars crashed on a level surface, assume the red car did not move, and assume that the pizza sign was not mounted on the car. Acceleration of gravity is 9.8m/s^2. Disregard air resistance.)

    2. Relevant equations
    Vf^2 = Vi^2 * 2a * deltaX?
    I'm sure there is more, but I first need to figure out where to start.

    3. The attempt at a solution
    I drew up this diagram in photoshop and uploaded it to flickr:

    I decided to first find the time that it takes for the sign to hit the ground. I then broke up the signs properties into x and y components. I used the equation listed above to find final velocity in the y direction which came out to be 5.36m/s. I am now stuck. I'm not even sure that I started it correctly. Any help from here would be greatly appreciated!
    Last edited: Nov 4, 2009
  2. jcsd
  3. Nov 4, 2009 #2


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    Gold Member

    The pizza sign is a clue to how fast the car was travelling when it hit the red car. Therefore you need to find its initial velocity.
  4. Nov 4, 2009 #3
    That's what I am trying to do. Once I get further I will update this thread. Thanks.
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