Asked by Dee

A vehicle is travelling at 25.0 m/s. It brakes provide an acceleration of -3.75 m/s^2[forward]. What is the driver's maximum reaction time if she is to avoid hitting an obstacle 95.0 m away?
the answer is a number less than 0.5 second. can you tell me the exact number and can you show me how to solve it?

Answers

Answered by drwls
The BRAKING time to stop is
T = 25/3.75 = 6.667 s

The distance travelled while decelerating is:
Vaverage*T = (1/2)(25)*6.667 = 83.33 m

She can travel only 95-83.3 = 11.7 m before applying the brakes.

Her reaction time must be t = 11.7/25.0 = 0.47 seconds or less, since 11.7 m is the maximum distance she can travel, at 25 m/s, before braking.
Answered by no
physics is hard
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