posted by Leewillikers .
An 9000 test car travels 40.5 before stopping from an initial speed of 25.7 on dry horizontal pavement with its wheels locked.
a)Make a free-body diagram of this car while it is slowing down.
b) What external force causes it to slow down?
c)Assuming constant acceleration, find the magnitude of the force in part A.
Your numbers require dimensions. That is one of the first things you should have learned.
With wheels locked, you should have a pretty good idea of the dominant decelerating force. There are going to be tire skid marks.