Lesson: Chapter 5 — Friction

Solving friction problems 3 of 7 Reset answers

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Question 3

A block is sliding along a table. It is pulled horizontally with a force of 30 N, and the dynamic friction between the block and the table is 12 N. What is the unbalanced force on the block?

A 42 N B 12 N C 30 N D 18 N

The right answer is the one marked above.

18 N.

unbalanced force = applied force − friction

30 − 12 = 18 N

42 N comes from adding instead of subtracting. Friction acts against the motion, so it always comes off the applied force, never adds to it.

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