A car of mass M brakes for 40m along a level road before stopping. The coefficient friction between the tires and the road is 0.7. What was the car's initial speed when it started to brake?
i) Draw a force or free body diagram.
ii) Find the components of the forces in your coordinate system.
iii) Write out Newton's 2nd law in component form.
iv) Solve these and find the acceleration and the initial speed.