Where does the energy go? Let's look at an example to see what happens to energy in an inelastic collision. A pickup truck with mass 1.80 x 103 kg is traveling eastbound at +17 m/s, while a compact car with mass 9.00 x 102 kg is traveling westbound at 717 m/s. The vehicles collide head on, becoming entangled. _, "'2 i 3 '3 (0 Find the initial kinetic energy (in J) of the system consisting of both vehicles. 390690 J J Correct. This is the combined kinetic energy of both vehicles before the collision. We find this by calculating the kinetic energy of each vehicle before the collision and adding them. J Find the speed (in m/s) of the entangled vehicles after the collision. y J Correct. This is the speed of the entangled vehicles after the collision. This is found by conservation of momentum, where the system after the collision has the total mass of both vehicles. rn/s Find the change in kinetic energy (in J) of the system consisting of both vehicles. 86490 x x Incorrect. Use the equation for kinetic energy and the final speed of the entangled cars to find the final kinetic energy of the system before finding the change in kinetic energy. J You should find above that the kinetic energy after the collision is lower than it was before collision. Where did the energy likely go? It is dissipated as heat and sound as the vehicle frames are damaged. 0 It is dissipated due to air resistance. 0 The energy simply disappears. Conservation of energy does not apply in inelastic collision, J J Correct. Since the cars became entangled, it is likely that the energy was lost as the vehicles were damaged. It's important to remember that in an inelastic collision, the kinetic energy before the crash is greater than afterwards