You are driving your car, and the traffic light ahead turns red....

Question

You are driving your car, and the traffic light ahead turns red. You apply the brakes for 2.22 s, and the velocity of the car decreases to +4.91 m/s. The car’s deceleration has a magnitude of 2.92 m/s² during this time. What is the car’s displacement?

Answer 1

Recall the basic equations for constant acceleration:

v = v₀ + at

s = s₀ + v₀t + ½at²

In this case, you have three known quantities: t, v, and a.

You can solve the first equation to find v_0.

Then you can solve the second equation to find s.

Be careful with signs: the acceleration is negative.

Answer 2

Displacement S = v₀t + at²/2 = 4.91·2.22 - 2.92·2.22²/2 = 3.705 m