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3 conceptual TEST questions

  1. Feb 27, 2009 #1
    1. a force is directed 20 degrees from the horizontal on a 2kg object. At the top of its projectory, what is the magnitude of the force acting on the object.

    I said 19.6 N, because the only force acting there would be gravity, right? so 9.8*2 = 19.6 N

    2. an object that weighs 3m explodes and into two pieces that weigh 2m and m. Which is the only statement that can be true?

    I narrowed it down to two choices

    1. the pieces fly off perpendicular to one another
    2. the smaller piece has a velocity two times greater than the larger piece.

    I chose the 2nd choice

    3. A car is moving east. A second car is traveling due north. During the collision, the 2nd car has a resulting velocity due south (opposite direction). What is the only possible direction of the 1st car?

    A graph was given with choices that the 2nd car can move west, east, north, north west, or north east. The conservation of momentum obviously comes into play. I screwed up here and chose that it goes west.
  2. jcsd
  3. Feb 27, 2009 #2


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    Homework Helper

    Welcome to PF.

    I'm not sure exactly about 1) because I don't understand how long the force was applied and whether it became a projectile.

    2) looks right.

    3) Yes if the north car reverses, the other has its momentum to the east still and twice the momentum of the north bound to the north, in order that the momentum in x,y remains constant.
  4. Feb 27, 2009 #3
    thank you! now I can at least breath a little easier.

    the question for the first was pretty simple. a force is applied at 20 degrees relative to the horizontal on a 2kg object. The object follows a parabolic trajectory. What is the magnitude of the force acting on the object at the top its trajectory.

    Since the acting force doesnt act anymore during the parabolic motion and the only force at the top of the parabola is the force due to gravity, the magnitude at the top has to be f=ma or (2)(9.8)= 19.8 N. Any ways, thats what im thinking there. thank you for your help.
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