The Disc Brakes of a High Performance Car Are Often

Multiple Choice

The disc brakes of a high performance car are often made of carbon fiber instead of iron,thereby reducing the mass.If both types of discs are of the same size and shape,and each iron disc has a mass of 4 kg and each carbon disc has a mass of 1 kg,what is the reduction in rotational kinetic energy at 72 km/h if all the four iron discs in the car are replaced with carbon discs?

A) 300 J
B) 400 J
C) 800 J
D) 1200 J
E) 1600 J