Answer:
magnitude of the force exerted on the wall is 2100 N.
Step-by-step explanation:
given data 
rate = 50.0 kg/s
speed = 42.0 m/s
solution 
momentum is reduced = zero
so final speed v = 0
so relation between the force and the momentum is express as
Force = 
 ...............1
Force = 
 
put here value and we get 
Force = 
 
Force = 2100 N
so that magnitude of the force exerted on the wall is 2100 N.