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Homework Help: Find velocity of puck and octopus

  1. Jan 11, 2005 #1
    Could someone help me with the set up of these problems?
    1.)A hockey puck, mass 0.120 kg, moving at 30.0 m/s, strikes an octopus thrown on the ice by a fan. The octopus has a mass of 0.275 kg. The puck and octopus slide off together. Find their velocity.
    2.)A 0.21-kg ball is placed on a compressed spring on the floor. The spring exerts an average force of 2.7 N through a distance of 13 cm as it shoots the ball upward. How high will the ball travel above the release spring?
  2. jcsd
  3. Jan 11, 2005 #2


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    What do you think ? Give it your best shot.
  4. Jan 12, 2005 #3

    How about helping us to know WHERE your problem is while you were TRYING to solve the problem? :tongue2:
  5. Jan 12, 2005 #4
    For the first one, try using the Principles of Conservation of Momentum (do you know anything about this law? if yes, that part should be really easy! )

    For the second one, I assume that the ball moves in a vertical direction upwards.
    You are given the average force exerted by the spring on the ball and the distance that the ball moves(13 cm) as the spring decompresses until it releases the ball. From that, you can determine the acceleration and in turn find the final speed at the moment the ball leaves the spring.
    And then, you can re-use the equation of motion to find the height to which the ball reaches :approve
  6. Jan 12, 2005 #5


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    For the second problem, it is simpler to use "work" rather than try to calculate the acceleration. The work done by the spring is the average force times the distance the spring moves the ball. That will be equal to the kinetic energy of the ball at the time it leaves the spring. Convert that to potential energy to see how high the ball will go.
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