Question

Two trains one travelling at $15m{s}^{-1}$ and other at $20m{s}^{-1}$ are headed towards one another a straight track. Both the drivers apply brakes simultaneously when they are $500m$ apart. If each train has a retardation of $1m{s}^{-2}$, the separation after they stop is

• A. $192.5m$
• B. $225.5m$
• C. $587.5m$
• D. $155.5m$

Answer 1

The correct option is C $587.5m$

To find stopping distance

For first train

$v^2-u^2=2as$

$0-{15}^2=-2\times 1\times s$

$⟹s=\frac{225}{2}m=112.5m$

For second train

$v^2-u^2=2as$

$0-{20}^2=2\times (-1)\times s$

$⟹200m$

$\therefore$ Separation $=500+200-112.5$

$=300-112.5$

$=587.5m$