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Velocity problem did i do it right?

  1. Sep 11, 2008 #1
    1. The problem statement, all variables and given/known data
    a cart is pushed along a straight horizontal track
    a.) in a certain section of its motion, its original velocity is +3 m/s and it undergoes a change in velocity of +4 m/s. does it speed up or slow down in this section of motion? is its acceleration positive or negative?

    b.) in a certain section of its motion, its original velocity is -3 m/s and it undergoes a change in velocity of +4 m/s. does it speed up or slow down in this section of motion? is its acceleration positive or negative?

    c.)in a certain section of its motion, its original velocity is +3 m/s and it undergoes a change in velocity of -4 m/s. does it speed up or slow down in this section of motion? is its acceleration positive or negative?

    d.) in a certain section of its motion, its original velocity is -3 m/s and it undergoes a change in velocity of -4 m/s. does it speed up or slow down in this section of motion? is its acceleration positive or negative?



    2. Relevant equations



    3. The attempt at a solution

    a.) it increases and acceleration is +
    b.) it decreases and acceleration -
    c.) it decreases and acceleration is -
    d.) it increases and acceleration is +
     
  2. jcsd
  3. Sep 11, 2008 #2

    LowlyPion

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    Homework Helper

    Put the velocities out on a number line. Negative to positive, left to right.

    Any change when you go from initial to final that is left to right is positive change. To the right is negative change.

    Look at your problem again.
     
  4. Sep 11, 2008 #3
    okay, so by looking at it again i got
    a.) it increases and acceleration is +
    b.) it increases and acceleration -
    c.) it decreases and acceleration is -
    d.) it decreases and acceleration is +

    i changed the accelerations because isnt it that when the signs are the same, that means that acceleration is + and when the signs are different the acc. is -?
     
  5. Sep 11, 2008 #4

    LowlyPion

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    It's the direction of the change in velocities. If velocity decreases, then acceleration is in the "decreasing" direction - i.e."-" - whether or not the signs of velocity are positive or negative. It's whether the differences are + or -.

    Like housing values are determined by Location. Location. Location.
    Here it's Direction. Direction. Direction.
     
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