# Homework Help: Determine the natural frequency

1. Feb 24, 2017

### cxz7410

1. The problem statement, all variables and given/known data
Determine the natural frequency in Hz of the system sketched below given the following values:
Mass m=4kg Spring stiffness k=28kN/m Length a=121mm Length b=93mm

2. Relevant equations
ω=(k/m)^0.5

3. The attempt at a solution
so probably I need to find m
should I multiply 4*9.81*(0.93+1.21)?

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Last edited: Feb 24, 2017
2. Feb 24, 2017

### Staff: Mentor

m is used for the mass already, you shouldn't reuse symbols for different things. Where can you use that formula?

What is the potential energy of the system (and its components) if the spring is extended by a length x?

3. Feb 24, 2017

### haruspex

That formula only applies to the usual simple arrangement of spring and mass.
While it is true that you can make your quoted formula work by finding an "effective" mass for the m in it to represent, it is not at all obvious how to find it. Indeed, that approach would be backwards. You need to find the equation of motion from first principles. Having found that you will see what the effective mass is in this arrangement. It is a very bad idea to go making wild guesses.