# Hookes Law, Finding A Springs Constant

1. Jan 5, 2014

### kcrawshaw

A spring extends by 10cm when a mass of 100g is attached to it. What is the spring constant? (calculate your answer in N/m)

I have done this so far but I don't feel that it is right as the Force (F) is in grams and not Newtons:

F = K x E
100 = K x 0.10
100 ÷ 0.10 = 100
K = 100 N/m

Is this right or have I gone wrong somewhere?
Thanks

Last edited: Jan 5, 2014
2. Jan 5, 2014

### Staff: Mentor

What's the weight (in Newtons) of a 100 g mass? (Always convert everything to standard units.)

3. Jan 5, 2014

### oneplusone

$F- kx$
100g = 100*10 = 1000 Newtons of force.

$1000 = -k (-0.1) \implies k = \boxed{10 000}$

4. Jan 5, 2014

You'll need to convert the weight from g to kg; right now you have the units in (g*m/s^2)/m
N/m is (kg*m/s^2))/m where the unit of Newtons is kg*m/s^2

5. Jan 5, 2014

### Staff: Mentor

This is incorrect.

Please allow the OP to solve the problem for themselves.