1. The problem statement, all variables and given/known data The van travels over the hill described by y=(-1.5(1/1000)x^2 + 15)ft. If it has a constant speed of 75ft/s, determine the x and y components of the van's velocity and acceleration when x=50ft. http://img215.imageshack.us/img215/3631/dynamcs.jpg [Broken] 2. Relevant equations 3. The attempt at a solution I took the derivative of the equation of the hill in order to find the equation for the velocity in the Y direction. The result was: Vy=(-3x/1000) This bothered me, seeing as it would make the Y velocity always negative. So when x=50, Vy=-.15ft/s and since the problem states that the van has a constant velocity of 75m/s I used Pythagorean to solve for the velocity in the x direction (75^2)-(-.15^2)=Vx^2 This gives me a value of Vx=74.9 When I plug these numbers into the answer (we use an online homework system) It tells me that the first term (74.9) has an incorrect sign, yet when I change the sign the problem is simply wrong. Unless the program is trying to tell me I messed up a sign in my calculations. So after getting stuck on this problem I moved on to the next part: finding the x,y components of the acceleration at x=50. And it's been a few hours and I'm stumped.