physics
posted by julie .
A 215 g mass is attached to a spring and executes simple harmonic motion with a period of 0.250 s. If the total energy of the system is 2.30 J.
(a) Find the force constant of the spring.
135.81 N/m
(b) Find the amplitude of the motion.
i just need help with what equation i should use. im stumped on this question.

The period is
P = 2 pi sqrt(k/m)
Use that and the mass to get the spring constant, k.
The total energy of the system is
(1/2) k X^2 = 2.30 J,
where X is the amplitude. .
Knowing that and k, solve for X.