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Finding force given constant velocity and mass?

  1. Sep 5, 2007 #1
    1. The problem statement, all variables and given/known data

    A man lifts a 2.2 kg stone vertically with his hand at a constant velocity of 1.5 m/s. What is the force exerted by his hand on the stone?

    2. Relevant equations

    F=ma (I would assume)

    3. The attempt at a solution

    I know that (9.81 m/s^2)x(2.2 kg) = 21.582 N (the weight and the normal force) and that the force exerted by the hand must be greater than that to make the stone rise...But when there is a constant velocity, isn't the acceleration 0? How would that work with F=ma?
     
  2. jcsd
  3. Sep 5, 2007 #2

    Dick

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    There are two forces acting on the stone, gravity and the force exerted by the hand. As you have correctly deduced, a=0. The F in F=ma is the sum of all of the forces. So what do you conclude about the sum of all the forces? The force exerted by the hand doesn't have to be greater than weight. It just has to be ____. Fill in the blank.
     
  4. Sep 5, 2007 #3
    Would the force exerted by the hand be equal to the weight? That was what I thought at first, but then I got all confused thinking about net forces and normal forces and acceleration... :)

    I have another question that is confusing me, should I post a new thread or use this one?
     
  5. Sep 5, 2007 #4

    Dick

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    That would be correct. If it's a quick similar one you can do it here. If it's a whole new line of inquiry, I'd start another one.
     
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