At train moving with a speed of 100 km/h can be stopped by brakes after atleast 15m. What will be the minimum stopping distance, if the same train is moving at a speed of 120 km/h?

Explanation

Speed = 100 km/h
Initial, Velocity `u=100xx(5)/(18)=27.7ms^(-1)`
Distance travelled = 15 m , Final velocity v = 0.
`therefore" Acceleration a"=-(u^(2))/(2s)`
`a=-((27.7)^(2))/(2xx15)=(771.6)/(30)=25.72ms^(-1)`
`a=25.72ms^(-2)`
For `u=120km//s=120xx5//18=33ms^(-4)`
Distance covered,
`s=-(u^(2))/(2a)=((-33)^(2))/(2xx25.72)=(1089)/(51.44)=21.17m=21m`