# Simple physics help pls

1. Oct 26, 2009

### skyguy

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. Oct 26, 2009

### Coreyh7988

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.

3. Oct 26, 2009

### skyguy

thanks... u safe me lots of trouble