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## Homework Statement

It's an oscillation problem. I have to find the FIRST time when the spring-mass system will have E (mechanical energy) = K (kinetic energy), if x(t)=12sin(5t+3,5). (t is time in seconds, x is lenghtof the system in cm).

## Homework Equations

E=1/2kA^2

K= 1/2kx^2

## The Attempt at a Solution

What I think: If E = K, there is no potential energy (U). So we are searching the first time when K will be maximal. I know that Kmax in a simple harmonic motion is when V is max. So, in the trigonometry circle : at π and 2π, 3, 4 etc. Since Φ start at 3,5, little after π, i think that the first time will be at 2π rad (where K is max). But when i use 2π in the equation [ x(t)=12sin(5t+3,5)], i come up with a negative time...

Thanks for helping me sorting this out!