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Simple physics help pls

  1. Oct 26, 2009 #1
    need some help to refresh my memory.

    was just doing some specification checking... when the motor is to lift a weight...

    let say the weight is to be move at 2m/s with 2sec when it start... and stay at 2m/s throughout after that...

    the initial force would be F = ma + (Watever force it need to overcome)
    where ma = m (dv/dt) ... simple

    ok now the question... after it have reach the 2m/s velocity should the force F be
    F = (watever force it need to overcome) only ???... coz i don't need any more acceleration and just constant speed
     
  2. jcsd
  3. Oct 26, 2009 #2
    Well, yes lets assume you want to lift an object with just a pulley. The initial lifting of the object as you stated would need more than the objects gravitational force. Then to have the object lift at a constant velocity the force would just need to be equivalent to the gravitational force upward. The mass would then have no acceleration/net force and thanks to the laws of inertia would be able to continue travelling upward at a constant velocity.
     
  4. Oct 26, 2009 #3
    thanks... u safe me lots of trouble
     
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