The part of the that's responsible for most of the fraction of incoming light is the

-3m/s²

2400N

Explanation:

Given parameters:

Mass of tram  = 800kg

Time taken   = 6s

Constant speed  = 18m/s

Unknown:

deceleration  = ?

force on brake = ?

Solution:

Deceleration is the opposite of acceleration. This is the rate of change of velocity with time;

    Deceleration  =

V is the final velocity = 0m/s

U is the initial velocity  = 18m/s

t is the time taken

   Deceleration  =  = -3m/s²

Force needed to to stop the tram;

        Force  = mass x acceleration

   Insert parameters and solve;

        Force  = 800 x 3  = 2400N