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Two cars of equal weight and braking ability are travelling along the same road but combined with other factors it could mean the difference between life.
This is easily explained saying that the frictional force between the books and the paper isn't big enough to produce a displacement in the books. The displacement in the books doesn't happen because the frictional force between the books and the surface they are standing on is bigger than the paper's one.
Answer:
Good question to ask in physics, sir maam