How do you go about solving this problem?

Question

Superman (mass = 78.0 kg) stops a train (mass = 18619 kg) headed for a broken bridge. The train was
initially traveling at 60.0 km/h. During the constant deceleration, the passengers experience an average
horizontal force of 0.410 their own weight. How long does it take for the train to come to a stop?

Answer 1

The horizontal deceleration is a = -0.410*g where g = 9.8 m/s^2. The minus sign is because the deceleration is in a direction opposite to the intitial velocity.

V = Vo + a*t where V = 0