Lesson: Chapter 5 — Friction

Solving friction problems 1 of 7 Reset answers

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Question 1

A block of weight 40 N rests on a table. The limiting friction between them is 12 N. The block is pushed horizontally with a force of 7 N. What is the frictional force on the block?

A 40 N B 12 N C 5 N D 7 N

The right answer is the one marked above.

7 N. First ask whether it is moving:

7 N < 12 N, so it stays at rest

friction = applied force = 7 N

12 N is the tempting answer, but that is the most friction these surfaces could supply. Static friction only ever supplies as much as it needs.

Answer the question to continue.