Passive forces and Newton's laws

[tica86]

A block can move with constant velocity even though it has an applied force. Newton's first law is NOT violated.

We were going over this in class today but I don't understand it, why is Newton's first law not violated?

What applied force would you need to keep the block moving with a constant velocity that is twice as large as before?

I also have the following questions that I just want to make sure I'm doing correctly:
What is the magnitude of the unknown force?
a. A 1.0 N weight is hanging at rest from a chain with weight of 0.5N. Is magnitude=1.0+0.5N?

b.A 1.0 N weight is hanging at rest from a string with negligible weight. Magnitude =1.0+0?

c.A spring with negligible weight and a hanging weight of 1.0 N. Magnitude=1.0+0??

 

[willem2]

If the sum of all forces acting on the block is not 0, it can't move with a constant velocity.
There probably is a friction force.
Note that constant velocity means, that the direction is constant as well as the magnitude.