A 1kg particle is in a potential given in joules by U(x)=4x2+5x-3, where x is in meters. The particle is initially at position x=1m and moving with velocity v=6m/s in the +x direction. Find the position when the particle first comes to rest. Here is my train of thought F(x)= -dU/dx so F(x)= -8x-5 Then i figured since F=ma (mass is 1kg) that F(x)=a i used the equation 2a(xf-xi)=v2^2-v1^2 to solve for acceleration which i plugged into above equation using v2=0, v1=6 and xi=1 this gave me -8x-5= -36/(2x-2) -16x^2 + 6x + 46=0 then i solved the quadratic, rejected the negative answer since the particle is initially at 1. My answer is 1.89m which is wrong. can someone please tell me what i'm doing wrong and point me in the right direction?