# Homework Help: OSCILLATING my brain

1. Aug 31, 2014

### BusyEarning

i know this problem is posted on this forum somwhere else but i cant quite understand thanks in advance

1. The problem statement, all variables and given/known data

A mass of 0.3 kg is suspended from a spring of stiffness 200 N m–1. If
the mass is displaced by 10 mm from its equilibrium position and
released, for the resulting vibration, calculate:

the maximum velocity of the mass during the vibration

2. Relevant equations

F=kl

3. The attempt at a solution

so far i am thinking that i need to use hookes law as follows so i can get the amplitude
F=k(l+x)

F= mg = 0.3 kg x 9.81 = 2.94 N
k = 200 Nm-1
l = static spring reflection = 2.94/200 = 0.01
x = displacement due to external force = 10mm

so the amplitude would be l + x = 10.01mm?

do i need to take into account the extra extension when attempting the solution or is it just f/k =l
or do i need to use f/k = l + x to calculate the amplitude

any help would be appriciated

Thanks

2. Aug 31, 2014

### Simon Bridge

The oscillations are around the equilibrium position, not the unstretched length.
Remember you have gravity as well as the string acting on the mass.

I would use conservation of energy for this problem.
For instance, at the top of the motion, the energy stored in the spring has been changed into gravitational potential energy.