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Free Falling Body in Vacuum

  1. Oct 9, 2014 #1
    • Warning: The Posting Template must be used when startng a thread in the Homework areas
    Here is an unsettling question from a practice set that I've been working on today. Unsettling because the answer key contradicts my answer so I need a second thought.

    A pingpong ball and a golf ball are dropped in a vacuum chamber from the same height and at the same time. When they have fallen halfway, they have the same

    A. Potential energy
    B. Kinetic energy
    C. Acceleration
    D. Velocity

    My answer is C. Acceleration since this is what I've learned from college physics. But the answer key says it is D. Velocity. So I'm quite confused.

    Help me guys. Thank you in advance! :)
  2. jcsd
  3. Oct 9, 2014 #2
    I think there are two answers of this question.
  4. Oct 9, 2014 #3


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    Both the accelerations and the velocities are the same.

  5. Oct 9, 2014 #4

    Simon Bridge

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    Do not believe something just because you are told it - is there a good reason from the laws of physics to believe that C is correct?
    What are your reasons from physics for rejecting each one of the other answers?
    As you go through the reasons, the correct answer should occur to you.
  6. Oct 9, 2014 #5
    Thanks guys! They have the same acceleration so the change in magnitude of velocity must be the same at any given time. It's just this is a question from an admission test and I find it unsettling that the machine will mark one correct and the other wrong...
  7. Oct 9, 2014 #6

    Simon Bridge

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    Homework Helper

    Yes, that is a common flaw in machine mediated tests.
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