What Force is Needed to Maintain Constant Velocity?

[bionut]

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

... I am stuck ... all I can think of is F = mv (velocity being constant therefore its not accelearting? ) F = 20 kg x 2ms/ = 40Nm (j) ?

 

[PeterO]

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

... I am stuck ... all I can think of is F = mv (velocity being constant therefore its not accelearting? ) F = 20 kg x 2ms/ = 40Nm (j) ?

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.

 

[kru_]

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.