Question

the motorcycle is moving with a velocity of 90 kilometre per hour and it takes 5 seconds to stop after the brakes are applied calculate the force exerted by the brakes on the motorcycle if its mass along with the rider is 200 kg

Answer 1

initial velocity(u) = 90 km/s = 25 m/s
time (t) = 5 sec
mass (m) = 200 kg 
final velocity (v) = 0 m/s
v = u + at 
0 = 25 + a * 5
-25 = 5 a
-5 = a
Therefore acceleration = -5m/s²
Force = mass * acceleration 
F = 200*-5
F = -1000 N
I hope it helps………..

Answer 2

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.
-5= a
Now, force exerted = product of mass and acceleration
= 200* -5
= -1000 N