Answer:
Explanation:
Given
mass of bus along with travelers travelling in North direction is 
speed of bus towards North 
mass of bus travelling in South direction is 
speed of bus 
mass of each Passenger in south moving bus 
Momentum of North moving bus



Momentum with south moving bus


For total momentum to be towards south
should be greater than 0
thus for least value of n



2 min = 120 sec
120/15 = 8
The black horse represents 8 seconds.
the action and reaction do not lead equilibrium if action and reaction force react on different objects