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Forces using Newtons Second law

  1. Oct 29, 2011 #1
    1. The problem statement, all variables and given/known data
    A bullet fired into wet clay will decelerate fairly uniformly. If a 10 g bullet hits a block of clay at 235 m/s and comes to rest in 17 cm, what average force does it exert on the block? [Hint: From the fact that the bullet goes from vi to 0 in a distance s, you can find aav and with that Fav.]


    2. Relevant equations
    ƩF=mg


    3. The attempt at a solution
    These are all of the answers I have gotten wrong
    46.94 N

    13.82 N

    23.5 N
     
  2. jcsd
  3. Oct 29, 2011 #2

    PhanthomJay

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    The hint is telling you to use one of the kinematic equations to solve for the acceleration of the bullet. Once you solve for it, then use Newton 2 in the horizontal direction to solve for the net force acting on it in the horizontal direction.
     
  4. Oct 29, 2011 #3
    how do you find the acceleration of the bullet
     
  5. Oct 29, 2011 #4

    PhanthomJay

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    Look up and memorize the kinematic equations for constant accelertion. pick the one that works best for the given problem. The bullet travels a given distance in the block with a given initial speed. It's final speed is 0 after it travels the given distance in the block.
     
  6. Oct 29, 2011 #5
    is it possible for the acceleration to be negative
     
  7. Oct 29, 2011 #6

    PhanthomJay

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    Why sure. Like when you hit the brakes, the car is moving forward in a positive direction, but the acceleration is in the negative direction, with the braking force acting in the negative direction to slow the car down. If you then hit the gas pedal, the car speeds up again and the acceleration is positive.
     
  8. Oct 29, 2011 #7
    can the force be negative i got -1624.26
     
  9. Oct 29, 2011 #8

    PhanthomJay

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    Yes, you are quite right :approve:, but don't forget the units and round off the answer to say F = -1600 N.
     
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