1. The problem statement, all variables and given/known data What net force would be necessary to stop an automobile of mass 1000kg traveling initially at a speed of 15m/s in a distance equal to the diameter of a dime, which is 1.8cm ? 2. Relevant equations 3. The attempt at a solution The force required to stop the car is given by F = dp/dt. Change in momentum = mv - mv0 As far as I can see, it's not possible for me to determine a time in which this change in momentum takes place. I have been staring at it for ages and not making any head way. Thanks for any help you can give.