A driver travelling at 30.0 m/s takes 0.500 s to react before braking. How far does the car travel during the reaction time, and what is the total stopping distance on dry concrete where braking alone needs 64.3 m?
A7.50 m during reaction and 71.8 m in total
B30.0 m during reaction and 94.3 m in total
C15.0 m during reaction and 64.3 m in total
D15.0 m during reaction and 79.3 m in total
Answer & Solution
Correct answer: D. 15.0 m during reaction and 79.3 m in total
1. During the reaction time the acceleration is zero, so the velocity stays at 30.0 m/s.
2. Distance equals average velocity times time for that leg.
3. Substitute the values: (30.0 m/s)(0.500 s) = 15.0 m.
4. The braking distance on dry concrete is 64.3 m.
5. Add the two legs: 64.3 m + 15.0 m = 79.3 m.
6. Leaving the reaction leg out returns 64.3 m, the trap in one of the options.
_Source: OpenStax College Physics (CC BY 4.0), Ch 2 "Kinematics", section 2.5 Motion Equations for Constant Acceleration in One Dimension_
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