What Are the Amplitude and Period of the Mass-Spring System?

[teenholiday]

A massless sping of spring constant k=74 N/m is hanging from the ceiling. A 490g mass is hooked onto the unstretched spring and allowed to drop. Find the amplitude and the period of the resulting motion.

Attempt:
F= -kx

x= A cos (wt)
w = sqrt(k/m) t

I'm trying to solve for A, but how do I get rid of the t variable?


Thanks

 

[rock.freak667]

Find $\omega$ and you could use the fact that at max displacement from the equilibrium posistion, velocty=0.