D. A body at rest tends to remain at rest. 6. Quantum mechanics is necessary to describe the behavior of the following objects, except A nucleus of a heavy metal atom. B. diatomic oxygen (two bound oxygen atoms). C. a chunk of ice traveling at a significant fraction of light speed D. electrons orbiting a helium nucleus. 7. A force of 40 N accelerates a given mass by 20 m/s2. If the mass is doubled and the force is halved, what will be the new acceleration? F=ma (Ask for help on this one) A. 5 m/s2 B. 10 m/s2 C. 20 m/s2 D. 80 m/s2 S. A boy shoves a 2.0-kg brick on the ground with his foot. He applies a constant force of 10.0 N. Meanwhile, friction with the ground opposes the motion with 11L 9 E-m​