1. The problem statement, all variables and given/known data The graph shows the speed as a function of time for a minivan, coasting on neutral along a straight, level road, loaded with windsurfing equipment and towing a boat. The total mass is 2500 kg, weight= 5512lbs. Find the size of the force due to wind and rolling friction when the van speed is 44.17 mph. (1 mph=0.447m/s) 2. Relevant equations F=ma 3. The attempt at a solution I don't think anyone needs to see the graph to understand my problem. Well I hope. I understand that a= delta v/delta t. But whenever I use the equation I get an acceleration that does not work. Then I thought that since the equation wants the force at 44.17 mph, that I need to find the instantaneous acceleration. That's my problem: I don't know how to get the instantaneous acceleration. At 44.17 mph the time is at 19 s. Should I create a derivative. If so, how do I go about it? The answer for this problem is 764 N Please tell me why my approach is incorrect.