a 2.00 kg frictionless block is attached to an ideal spring with force constant 300 N/m. at t=0 the spring is neither stretched nor compressed and the block is moving in the negative direction at 12.0 m/s. Find the amplitude, the phase angle, and write and equation for the position as a function of time. i used w=√(k/m) to find the angular frequency. i get w=12.25 rad/s then, i'm assuming that when x=0, the cos(θ) must equal zero, in the equation x=Acos(wt+θ) solving for θ i get θ=∏/2. after that i used v=-wAsin(wt+θ), to find the amplitude, which i got the amplitude of 0.98m I believe i got the phase angle and amplitude with the right concepts of simple harmonic motion, except i can't figure out how to get the right equation of x(t). i always thought x(t) was supposed to have a cos function in it, however the answer in my book says it is a sin function. If someone could explain this to me i would greatly appreciate it.