Question

A car moving with a speed of $40 \,km/h$ can be stopped by applying brakes after at least $2\,m$. If the same car is moving with a speed of $80 \,km/h$, what is the minimum stopping distance?

• A. 4 m
• B. 6 m
• C. 8 m
• D. 2 m

Answer 1

Answer: (C)

1 st case $v^2 - u^2 = 2as$
$0-\bigg(\frac{100}{9}\bigg)^2=2 \times a \times 2 [40\, km/h=100/9\, m/s]$
$a = - \frac{10^4}{81 \times 4} \, m/s$
2nd case : $0-\bigg(\frac{200}{9}\bigg)^2=2 \times \bigg(-\frac{10^4}{81 \times 4}\bigg) \times s $
$ [80\, km/h=200/9\, m/s]$
or $s = 8\, m.$