Question

On a foggy day, two drivers spot in front of each other when 80 metre apart. They were traveling at 70 kmph and 60 kmph. Both apply brakes simultaneously which retard the cars at the rate $5\left[m/s^2\right]$ Which of the following statements is correct?

• A. The collision will be averted
• B. The collision will take place
• C. They will across each other
• D. They will just collide

Answer 1

The correct option is A The collision will be averted

70 km to m/s $\to \left(70\times \frac{5}{18}\right)$
60 km to m/s $\to \left(60\times \frac{5}{18}\right)$
$V_{AB}=\left(V_A-V_B\right)=\frac{5}{18}\left[70+60\right]=\left(\frac{5}{18}\times 130\right)$
$a_{AB}=\left(a_A-a_B\right)=-\left(5+5\right)=-10m/s^2$
$v^2=u^2+2as$
$o=u^2-2\times 80\times 10$
$u^2⩽800\times 2=1600$ (To revert collision)
$1304.0⩽1600$