If the length of a 12cm spring increases to 20cm when a 10kg weight is hanging from it, what is the spring's constant?

1 Answer
Dec 9, 2015

1225Nm

Explanation:

A spring constant for a 'simple spring' is usually written as the k in:
F=kx

For force of a 10kg weight is calculated using gravity:
F=mg

F=109.8=98N

The x in the equation above is relative to the relaxed length of the spring. If the length of the spring is 12cm without any mass attached, we call this position zero and we can see that the additional length with the mass attached is 8cm longer.

We now know F and x and we can solve for k. Notice that the direction of the force is opposite to the direction of gravity, so the sign has changed.

F=kx

98N=k0.08m

980.08Nm=k=1225Nm