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Conceptual question regarding net force and velocity

  1. Feb 23, 2009 #1
    1. The problem statement, all variables and given/known data

    An object is moving to the right in a straight line. The net force acting on the object is also directed to the right, but the magnitude of the force is decreasing with time. The object will

    a) stop and then begin moving to the left.
    b) continue to move to the right, with its speed decreasing with time.
    c) continue to move to the right, with its speed increasing with time.
    d) continue to move to the right with a constant speed.

    The answer is c)

    2. Relevant equations

    3. The attempt at a solution

    My question is, can an object INCREASE in speed to the right at a DECREASING rate?

    If so, then I understand why the answer is c) However, I thought if an object was moving to the right and the net force was also moving to the right, that would mean the object was increasing, and since the net force is decreasing with time, then shouldnt that change how the object is moving? like doesnt that mean the object will begin to decrease in speed?

    Please explain to me the reason for the answer! (why it is c, and say, not b)

    Thank-you for any help!
  2. jcsd
  3. Feb 23, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Absolutely. As long as it moves to the right and it has an acceleration to the right, it's speed will increase. The rate at which the speed increases depends on the acceleration, which in turn depends on the net force.
  4. Feb 23, 2009 #3
    Newton's second law: F=ma. What happens, if there is a force acting on the object and what happens when you take it off?

    DocAl was faster! Damn!
  5. Feb 23, 2009 #4
    Thanks Doc Al!
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