When
a driver brings a car to a stop by braking as hard as possible, the
stopping distance can be regarded as the sum of two distances:

"reaction
distance", which is initial speed times reaction time, and "braking distance," which is the distance covered during
braking.

The following table gives typical values of these:

Initial speed (m/s) | Reaction distance (m) | Braking distance (m) | Stopping distance (m) |

10 | 7.5 | 5.0 | 12.5 |

20 | 15 | 20 | 35 |

30 | 22.5 | 45 | 67.5 |

(a)
What reaction time is the driver assumed to have?

(b)
What is the car's stopping distance if the initial speed is 251 m/s?