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Force with constant velocity?

  1. Oct 2, 2011 #1
    A 20 kg mass is sitting on the horizontal surface of a table top. Calculate the following Neglecting friction, calculate the force required to give the mass a velocity of 2ms.

    So far all I can think of is... F=ma

    m=20kg
    a=?

    a= Vf-Vi / t

    ..... im stuck ... all I can think of is F = mv (velocity being constant therefore its not accelearting? ) F = 20 kg x 2ms/ = 40Nm (j) ?
     
  2. jcsd
  3. Oct 2, 2011 #2

    PeterO

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    Homework Helper

    Not enough information.

    We do know that no force is necessary to maintain a velocity of 2 m/s.

    As to attaining a vel of 2 m/s from rest, we need to know how quickly we want that to happen - ie the acceleration.
     
  4. Oct 2, 2011 #3
    We have v = v_0 + a*t. And from F=ma we see that a = F/m. So, plugging in we can get v = v_0 + (F/m)*t. Since the block is at rest, v_0 is 0. We desire a velocity of 2m/s, so we plug in: 2 = 0 + (F/20)*t, or F = 40/t.
     
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