Hi, I have some troubles to understand the next step for the solution. If you need more informations, please let me know. 1. The problem statement, all variables and given/known data A moving vehicle of mass M is moving down an inclined plane of angle alpha with respect to the horizontal plane. What is the force indicated on the scale ? It is written pèse-personne between M and m. That's a scale (to weight people) 2. Relevant equations Acceleration of M on the inclined plane : a = g*sin(alpha) * (M/m + 1) 3. The attempt at a solution I started to try to find the acceleration of M on the inclined plane. I have the following forces acting on my moving vehicle : gravity (down), normal force (perpendicular to the inclined plane) and the weight of the mass m (it is not indicated but I assume that the scale doesn't have a mass). I separated the gravity components in parallel and perpendicular component and I get : Fg parallel inclined plane = (M+m)g * sin(alpha) The Fg perpendicular cancels out with normal force. I don't think I need it but that's the same of Fg parllel but with cosine. Then I have ma = (M+m)g * sin(alpha) which gives me a = g*sin(alpha) * (M/m + 1) (I can give the steps if needed). Now I am stuck. How can I find the normal force for m ? For m, I have the weight (down), the normal force (up), acceleration (right) and inertia (left). Those orientations are with respect to the moving vehicle and not the inclined plane. Am I supposed to break all the components in their parallel and perpendicular (to the inclined plane) components ? I am confused with this inclined and not inclined plane of the moving vehicle. The exercises we did before was an elevator (for the weight) and a moving vehicle on the horizontal axis (to introduce inertia). Thanks.