9. A 200-gram apple is thrown from the edge of a tall building with an initial speed of 20 m/s. What is the change in kinetic energy of the apple if it strikes the ground at 50 m/s? Ans. 210 J . 10. A solid disk flywheel (I = 200kg m2) is rotating with a speed of 900 rpm. What is the rotational kinetic energy? Ans. 888 kJ