Initial velocity, u = 90 km/h or 25 m/s.
Final velocity, v = 0 bcoz it stops
Mass = 200 kg
Now, force exerted by the brakes will be the acceleration they produce to stop the motorcycle.
Therefore we will use the formula, v = u+at
v= u+ at
0= 25 + a * 5
-25= a* 5
Therefore, force exerted by the brakes is -1000 N to stop the motorcycle.
Now, force exerted = product of mass and acceleration
= 200* -5
= -1000 N