Question

Two trains travelling on the same track are approaching each other with equal speeds of 40 m/s. The drivers of the trains begin to decelerate simultaneously when they are just 2.0 km apart. Assuming the decelerations to be uniform and equal, the value of the deceleration to barely avoid collision should be

• A. 11.8 $m/s^{2}$
• B. 11.0 $m/s^{2}$
• C. 2.1 $m/s^{2}$
• D. 0.8 $m/s^{2}$

Answer 1

Answer: (D)

0.8 $m/s^{2}$

Answer 2

Both trains will travel a distance of 1 km before to come in rest. In this case by using $v^{2} = u^{2} + 2as$

$\Rightarrow 0 = (40)^{2} + 2a \times 1000 \Rightarrow a = - 0.8\mspace{6mu} m/s^{2}$