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Homework Help: Projectile review

  1. Nov 27, 2011 #1
    1. The problem statement, all variables and given/known data

    Block I of mass 4.0 kg is on a horizontal, frictionless tabletop and is placed against a spring of negligible mass and spring
    constant 650 N/m. The other end of the spring is attached to a wall. The block is pushed toward the wall until the spring has been compressed a distance x, as shown above. The block is released and follows the trajectory shown, falling 0.80 m vertically and striking a target on the floor that is a horizontal distance of 1.2 m from the edge of the table. Air resistance is negligible.
    a.Calculate the time elapsed from the instant block I leaves the table to the instant it strikes the floor.

    b.Calculate the speed of the block as it leaves the table.

    c.Calculate the distance the spring was compressed.

    2. Relevant equations


    3. The attempt at a solution

    I really forgot how to do this. We are so far ahead of this unit, now, that I lost all my projectile motion mojo.
    I'm guessing you solve for time using the spring constant and one of the above equations, but that's all that I know. I'm really rusty in the projectile area. :(
  2. jcsd
  3. Nov 27, 2011 #2
    Since the block leaves the table with no initial downward motion you can solve the equation
    [tex] s = v_0t + \frac{1}{2}at^2 [/tex]
    Where [itex] s [/itex] is the distance from the table top to the floor and [itex] a [/itex] is the acceleration due to gravity.
    From this time you can use the same equation again using [itex] s [/itex] as the horizontal distance moved.
    For the third part try the work energy theorem :)
  4. Nov 27, 2011 #3
    Okay! I think I understand now! thank you!
  5. Nov 27, 2011 #4
    No problem, good luck! :)
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