An automobile with a linear momentum of 3.1×104 is brought to a stop in 5.5 .

What is the magnitude of the average braking force?

please put the units , do u mean 5.5 seconds ? if so then :

impulse = F t = M2 - M1

=> 5.5 F = 0 - 3.1 x 10^4

=> F = - 5636.36 N (negative since it's a resistant force)

mv/t=avg force you do the math (3.1x10^4)/5.5