Question

A vehicle moving at 60 kmph speed was stopped by applying the brake and the length of skid mark was 24.5 m. If average skid resistance of pavement is 0.7, then brake efficiency (%) of vehicle is

• A. 121.1%
• B. 172.9%
• C. 57.8%
• D. 82.5%

Answer 1

The correct option is D 82.5%

$V=60\times \frac{5}{18}=16.67m/sec$
$L=24.5m,f=0.7$
$L=\frac{v^2}{2gfb}$
where b = brake efficiency
$24.5=\frac{{16.67}^2}{2\times 9.81\times 0.7\times b}$
$b=\frac{{16.67}^2}{2\times 9.81\times 0.7\times 24.5}$
$b=0.8258=82.58\%$