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Which way will the ball swing?

  1. Jul 3, 2006 #1
    Can anyone help me with this?

    Assume that you are driving down a staight road at a constant speed. A small ball is tied on the end of a string hanging from the rear view mirror. Which way will the ball swing when you apply the breaks?
    a. forward
    b. backward
    c. it will not swing
    d. it depends how hard you apply the breaks

    thank you!!!
     
  2. jcsd
  3. Jul 3, 2006 #2
    Think about the individual speeds of the ball and the car. Obviously at, say, a steady speed of 60 km/h, both the car and the ball are travelling at that speed with respect to the road. If the car slows down (braking), what speed will the ball have in relation to it? Higher, lower, the same? Imagine the string isn't there and it's just floating in air, if it helps.
     
  4. Jul 4, 2006 #3
    Hint :Think pseudo forces .
     
  5. Jul 5, 2006 #4
    Think about it in a real context....... if you are in the car, and the brakes are applied, which way does it feel like you are moving?
     
  6. Jul 5, 2006 #5
    Inertia =)
     
  7. Jul 5, 2006 #6

    berkeman

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    Staff: Mentor

    Quiz question -- what if it is a very light balloon? Why is the motion different from a tennis ball?
     
  8. Jul 5, 2006 #7

    DaveC426913

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    Gold Member

    It isn't different. A light balloon will do the same thing as a tennis ball.

    Unless they meant a bouyant, helium-filled balloon... :devil:
     
  9. Jul 5, 2006 #8

    berkeman

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    Staff: Mentor

    Except, I got that question wrong on a physics test way back in undergrad. Their explanation at the time had to do with air pressure changes in the car.... You're saying I should have gotten that extra-credit question right? I'm gonna call up my old prof.....:approve:
     
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