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Q How is the braking efficiency of a goods vehicle calculated by measuring the stopping distance?

24th March 1967, Page 63
24th March 1967
Page 63
Page 63, 24th March 1967 — Q How is the braking efficiency of a goods vehicle calculated by measuring the stopping distance?
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Which of the following most accurately describes the problem?

AThis is done by using the formula v2 u2 + fS, where v equals the final velocity, u equals the initial velocity, f equals the acceleration rate and S equals the distance covered.

When applied to braking, thisformula will give a negative result denoting deceleration rather than acceleration. The formula can be reduced to a constant for each speed divided by the distance travelled. Thus the deceleration from

20 m.p.h. is shown as 431 and from 30 m.p.h. 968. The answers are given in feet

per second per second and if the result is put over 32.2 ft. per sec. per sec. and multiplied by 100 the braking efficiency as a percentage of the gravitational deceleration is obtained.

As an example, if a vehicle stops from 30 m.p.h. in 40 ft then the overall deceleration on

the stop is 96-8 which equals 24.2 ft. per 40

sec. per sec. The efficiency is then 24.2 100 which equals 75.5 per cent.