Calculating error

Dear Mike:
I read with interest the analysis of the timing of yellow traffic lights submitted by B.T. Johnstone in his letter that was printed in your paper last Wednesday (July 4).
I certainly agree with the point that was made regarding the ticketing of motorists at the intersection of King’s Highway and Keating Avenue. However, I feel obligated to correct an error in the following calculation.
Dr. Johnstone states: “In 0.5 seconds, a car travelling at 50 km/h travels 40 metres, and after moderate braking will still travel 20 metres.”
As any good “Fysix” student knows, a car travelling 50 km/h will travel 50,000 metres in one hour.
Since each hour contains 60 minutes and each minute contains 60 seconds, there are 3,600 seconds in one hour. Therefore, our law-abiding motorist, moving along at the speed limit of 50 km/h, will travel 50,000 metres in 3,600 seconds, or roughly 13.9 meters per second.
Let’s round this off to 14 m/s.
In 0.5 seconds, our “about to be ticketed” motorist then would travel about seven metres, not the 40 metres mentioned in Dr. Johnstone’s letter.
“Fysically” yours,
A. Hallikas


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