1. The problem statement, all variables and given/known data A particle P of mass m , which is on the negative x-axis. is moving towards the origin with a constant speed u. When P reaches the origin , it experiences the force F=-Kx^2, where K is a positive constant. How far does P get along the positive x-axis? 2. Relevant equations .5*m*v^2+V(x)=E(x) 3. The attempt at a solution dx/dt=[2*(E-V(x))]^.5 dV/dx=-F=Kx^2 ==> V=Kx^3/3 T0+V0=T1+V1 1/2*m*v^2+Kx^3/3=.5*m*u^2+0 since as the speed of particle increases V is zero. The problem with that explanation is, the speed is constant so the speed doesn't increase or decrease.