A car is travelling at 67mph (30m/s) when the driver steps on the brake slowing the car down at a rate of 3m/s2. How long and what distance will be required for the car to stop on dry pavement?

Answer 1

You must recognize that the problem is a constant acceleration problem, and you can use one of the kinematics equations of motion. You are given v_i = 30 m/s, v_f = 0 (stop), and a = - 3 m/s² (slowing down a positive velocity). You know 3 out 5 unknowns and there are 2 independent equations of motion - this is solvable. Pick the one that has no time in it:

2ad = v_f² - v_i² and solve for the displacement after setting v_f = 0

d = -v_i²/a

I'll leave you to plug things in.

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