Question

a test of a driver's perception reaction time is being conducted on a special testing track with wet pavement and a driving speed of 50 kph. when the driver is sober, a stop can be made just in time to avoid hitting an object that is visible 40 m. ahead. after a few drinks of san miguel beer, under exactly the same condition, the driver fails to stop in time and strikes the object at a speed of 30 kph. determine the driver's perception-reaction time after he was drinking. assume coefficient of friction is 0.60.

Answer 1

$d= v$₁ $\times tr$

$d=$ distance travelled for perception

$v$₁ = initial velocity

$tr$= perception time

$tr$ =$\frac{d}{v1}$ = $\frac{40}{50}= 0.8 seconds$

coefficient of friction $\mu$ = $\frac{force applied }{normal weight }$= $\frac{ma}{mg}$

0.6=$\frac{mg}{ma}= \frac{ma}{m\times 9.81}$

$a=9.81\times0.6=5.886 m/s$

$a$ (acceleration/deceleration) = $\frac{final velocity- initial velocity}{time^2}$

= $\frac{mg}{t}$ =$v$_v- $v$_u/t$2$

5.886= $\frac{0-30}{t^2}=equivalent = \frac{30}{t^2}$

t= $\sqrt[]{\frac{30}{5.886}} = 2.258 seconds$

total perception time for the unconscious driver is therefore prolonged as below;

t= 0.8 + 2.258

= 3.058 seconds