1. The problem statement, all variables and given/known data 1. Find the speed and acceleration when the kinetic energy is equal to half the potential energy 2. Find the minimum displacement between the points where the kinetic energy and acceleration are at half their maximum values 2. Relevant equations mv^2=.5kx^2 3. The attempt at a solution My correct harmonic equations x(t)=(√2/10)cos(10t+5∏/4) v(t)=-(√2)sin(10t+5∏/4) a(t)=-(10*√2)cos(10t+5∏/4) Got down to for part 1: arctan(√(1/2))=10t+5∏/4 All I want to know is if its acceptable to use the negative time value that comes from not shifting the output of the inverse tangent, to plug in for velocity and acceleration. Personally I don't see why not. And for part 2...what the bloody heck are they asking? I suppose I could find the displacements for each of those points and see when they get closest...I don't understand the goal of such a method though. If you want to see the whole problem I have attached it. Thank you for any help.