Consider the 1d motion of a body under the influence of the force given by F = -m*γ*vα. m is mass, γ is a constant of appropriate dimension, v is velocity and α is dimensionless constant. The value of α for which the motion will come to a stop in finite time is to be calculated. I solved the equation of motion given by v'' = -γ*vα and got an equation for t given by t = (1/γ)*(V01-α)/(1-α); V0 is the initial velocity. According to this, for all γ>1, time is finite. But the sign of t is negative. Why is this happening? Am I doing something wrong?