A mass of 2 kg oscillating on a spring with constant 4 N/m passes through its equilibrium point with a velocity of 8 m/s. What is the energy of the system at this point? From your answer derive the maximum displacement, x m of the mass.
When the mass is at its equilibrium point, no potential energy is stored in the spring. Thus all of the energy of the system is kinetic, and can be calculated easily:
K = mv 2 = (2)(8)2 = 64 Joules
Since this is the total energy of the system, we can use this answer to calculate the maximum displacement of the mass. When the block is maximally displaced, it is at rest and all of the energy of the system is stored as potential energy in the spring, given by U = kx m 2 . Since energy is conserved in the system, we can relate the answer we got for the energy at one position with the energy at another:
E f = E o
kx m 2 = mv 2 = 64
x m = = = 4 meters
We used energy considerations in this problem in much the same way we did when we first encountered conservation of energy- whether the motion is linear, circular or oscillatory, our conservation laws remain powerful tools.