posted by Jennifer .
You push a book on a table so that its velocity is constant. If the force that you apply is 15N. what is the force due to sliding friction? If you accelerate, so that the velocity is no longer constant is the force you are applying to the book greater or smaller than the sliding force? (Please answer in 100 words)
If and only if the applied (push) force equals the opposing (friction) force, there is no acceleration. That is the case in part 1 of your question. You need to apply a larger force than friction to accelerate. That answers part 2.