Suppose a particle is moving along the $x$ axis with velocity $v$. It starts at the point $-5$ and has constant negative acceleration $a$. You need to find what time the particle reaches the origin. My teacher solved this question, and used the kinematics equation Δx = v_0t+1/2 at^2 The quadratic had two roots, one of which was negative. What does the negative root mean? Is it extraneous (my teacher just said to ignore it)? Thanks.