A TRAIN SLOW FROM 72KM\H WITH A UNIFORM ACCELERATION OF 20M\S SQURE . HOW LONG WILL IT TAKE TO REACH 18KM\H ?
20 m/s^2 * 1km/1000m * 3600s/hr = 72 km/hr/s
So, it will take
(72-18)km/hr
---------------------- = 3/4 s
72 km/hr/s
or, you can convert km/hr to m/s and do it that way. Still, 3/4 second seems awfully fast braking for a train. Better check my math