Without newton’s third law of motion, what would an object sitting on a table do?

Without Newton's third law of motion, an object sitting on a table would continue sitting there, motionless, just we always see it do, and just as objects used to do before Newton ever developed his laws of motion.  

Getting the new law didn't change anything.  Just like everything else in Science, the new law was just a new description of how Nature works.  But it didn't change anything, because Nature doesn't care whether we understand how it works or not.

a.) is the correct answer.

explanation:

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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