We divide the thin rectangular sheet in small parts of height b and length dr. All these sheets are parallel to b. The infinitesimal moment of inertia of one of these small parts is

where

Now we find the moment of inertia by integrating from

to

The moment of inertia is

(from (-a/2) to

(a/2))
To calcculate the braking force of the car moving, we use Newton's second law of motion which relates the acceleration and the force of an object moving. The force of an object moving is directly proportional to its acceleration and the proportionality constant is the mass of the object. It is expressed as:
Force = ma
Acceleration is the rate of change of the velocity of a moving object. We calculate acceleration from the velocity and the time given above.
a = (10 m/s) / 5 s = 2 m/s^2
So,
Force = ma
Force = 1000 kg ( 2 m/s^2 )
Force = 2000 kg m/s^2 or 2000 N
Displacement = velocity * time
Just substitute the value, & solve the equation.
Hope this helps!