Lesson: Chapter 5 — Friction

5.2. Static, limiting and dynamic friction 6 of 9 Reset answers

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Question 6

A block starts to move when the pull reaches 18 N. The pull is then held steady at 18 N while the block slides, and the dynamic friction is 15 N. What does the block do?

A It slides at a constant velocity B It accelerates, because 3 N is left unbalanced C It slows down and stops again D It stays at rest, because friction has increased

The right answer is the one marked above.

It accelerates, because 3 N is left unbalanced.

18 − 15 = 3 N

Constant velocity is the tempting answer, but that would need the forces to balance. To slide it steadily the pull would have to be eased back to 15 N.

Answer the question to continue.