What does the negative sign in f = –kx mean? a)the displacement is in the opposite direction.
b)the spring constant is small.
c)the force is opposite the displacement.
d)the velocity is slowing down.

-ve sign shows that the displacement is in the opposite direction.  

Explanation:

The Hooke's law states that the force acting on the spring is directly proportional the displacement. Mathematically, it is given by :

or

F = -kx

Where

k = spring constant

-ve sign shows that the restoring force acts opposite to that of displacement. Hence, the correct option is (a) "The displacement is in the opposite direction".

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it