1. The problem statement, all variables and given/known data I am doing a practice problem out of the text book in order to improve my skills. The problem states the following: A free-rolling ramp has a weight of 120 lb. If the 80-lb crate is released from point A (top of the ramp), determine the distance the ramp moves when the crate slides 15 ft down the ramp and reaches the bottom pt B. I created an image for convenience: http://img689.imageshack.us/img689/2213/rampo.jpg [Broken] 2. Relevant equations Kinematics (maybe), Work-Energy and Impulse-Momentum equations apply. However we are mostly dealing with Work-Energy and Impulse-Momentum. If we do not have to use kinematics, then we should use work-energy. In other words, the simplest approach is the best. 3. The attempt at a solution I had trouble even beginning to attempt to solve the problem. My problem lies within the concept. I understand impulse and momentum, however I don't know why I can't extend it to problems like this (quirky ones). My first step was to establish a coordinate system. I chose a normal-tangential coordinate system. My positive x direction is parallel to the surface of the ramp and points in the direction the crate is moving down the ramp. My positive y-direction was chosen as perpendicular and "upwards" to/from the surface of the ramp. The next step I took was to draw the free-body diagrams of the crate and the ramp, separately, and then again together. On the crate, I had the weight force and the normal-force of the ramp on the crate. On the ramp, I had the normal force of the crate on the ramp, the weight of the ramp, and the reaction forces of the wheels. Next, I asked myself whether momentum is being conserved, and in which direction is it being conserved. This is where I came to a roadblock. I know there is a change in momentum because of the simple fact that the crate is released from rest, and ends up with some velocity. The problem wants me to find the distance the ramp travels... but how can the ramp even travel a certain distance if the normal forces between the ramp and crate cancel, and there is no friction to move the ramp in the other direction? I don't want to apply equations to the problem without knowing what is going on first. In other words, how do I proceed to solve this problem? I asked my instructor but he was very vague. He showed me a momentum equation which did still not make sense. I assume the problem involves relative velocities. Anyways, please help! And if my approach is wrong, please tell me how you would approach it and what coordinate system you would use?