What average force is required to stop a 1200 kg car in 7.0 s if the car is traveling at 100 km/h ?

This question can be answered with the basic laws of motion. Since the question is asking for FORCE, we know we must need this equation:



Since we know m but don't know a, we must find it using another equation. The one to use is:



where = the change in velocity. In this case the change comes out negative since the car is slowing down, and, you will notice that your answer will be a negative number to reflect this. Leave the negative symbol in your answer.

Now that you have a, simply solve for F above using F = m x a.