1. The problem statement, all variables and given/known data A linear harmonic oscillator is subject to friction(stokes). The Oscillator gets an Impulse at the time t = 0 at the rest position. What is the equation of motion for the time interval 0 - t0? 2. Relevant equations Friction force: Fr = -a * x'(t); a = constant (stokes friction) Impulse: F(t) = m *v0 / t0 (for 0 <= t <= t0) k = spring constant m = mass x(t = 0) = 0 (rest position at the time t = 0) x'(t = 0) = 0 (velocity at the time t = 0 is zero) 3. The attempt at a solution I have a little trouble with the impulse here. My attempt at a solution was this: m*x'' = -k*x - a*x' + m*v0/t0 ==> x'' + (a/m)*x' + (k/m)*x = v0 / t0 But my book claims that the equation really goes like this: x'' + (a/m)*x' + (k/m)*x = v0 / t0 * (1/m) Does somebody know why I am wrong and the book is right? I don't understand it, because I thought I needed a force(respectively acceleration) in above equation of motion. How does v0 / t0 * (1/m) fit into the equation, doesn't it have the wrong units?