1) 12 cm
2) 3 N
Explanation:
1)
The relationship between force and elongation in a spring is given by Hooke's law:

where
F is the force applied
k is the spring constant
x is the elongation
For the spring in this problem, at the beginning we have:


So the spring constant is

Later, the force is tripled, so the new force is

Therefore, the new elongation is

2)
In this second problem, we know that the elongation of the spring now is

From part a), we know that the spring constant is

Therefore, we can use the following equation to find the force:

And substituting k and x, we find:

So, the force to produce an elongation of 6 cm must be 3 N.