1. The problem statement, all variables and given/known data A red van came through and crashed into a green van. The driver of the red van claims that he was driving at a speed of 11 meters/second at the moment of the crash. You want to find out if his claim is true. a. the mass of the red van is 1000 kg b. the mass of the green van is 800 kg c. the length of the skid mark from the red van is 20 meters d. the length of the skid mark from the green van is 2.5 meters e. the red van was moving at 8 meters/second when the crash happened f. the coefficient of kinetic friction for the skidding is 0.4 1. Tell how much work the brakes did on the red van. 2. What was the change in energy of the red van before the crash? 3. What was the red van's initial kinetic energy? 4. Is the driver's claim correct? 2. The attempt at a solution I don't see a use for most of the data given for the green van, but here are my calculations: Frictional force = coefficient of friction * normal force Ff = 0.4 * 1000 * 9.8 = 3920 Work = -Ff * d W = -3920 * 20 = -78,400 J ---> work done on red van KEf = 1/2mv^2 KEf = 1/2 * 1000 * 8^2 = 32,000 J W = kinetic energy change W = KEf - KEi -78,400 = 32,000 - KEi KEi = 46,400 J ---> initial kinetic energy of red van And since we don't know the initial velocity... KEi = 46,400 46,400 = 1/2mv^2 46,400 = 1/2 * 1000 * v^2 v^2 = 92.8 initial velocity is app. 9.63 meters/second ---> the driver was wrong about going at 11 m/s The change in kinetic energy is 32,000 - 46,400 = -14,400 J.