The brakes on your car can slow you

The brakes on your car can slow you at a rate of 5.2 m/s^2. (a) If you are going 137 km/h and suddenly see a state trooper, what is the minimum time in which you can get your car under the 90 km/h speed limit?

Solution:

Note that the acceleration will be negative because the car is slowing down. To solve this question, we will use the following equation:

v=v_0+at where v is final velocity, v_0 is initial velocity, a is acceleration and t is time.

We will isolate for t and substitute the values given to us in the question:

t=\frac{25m/s-38m/s}{-5.2m/s^2}

t=2.5s

Therefore, the minimum time in which you can get your car under the 90 km/h speed limit is 2.5 seconds.

This question can be found in Fundamentals of Physics, 10th edition, chapter 2, question 30.