1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    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


    User Avatar
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook