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Physics Review Question Unit: Mechanics Year: 1991 Question#: 57 Question: A box at rest on a level floor is being acted upon by a variable force. Compared to the force required to start the box moving, the force needed to keep it moving is (1 ) less (2 ) greater (3 ) the same What is this question really asking? Explanation by: PeterM [ Return to question menu ] Answer 1 less CORRECT The force used to get the box moving is equal but opposite to the static friction. After the box starts moving it turns into kinetic (sliding) friction, which is less than static friction. return to top Answer 2 greater INCORRECT It takes more force to get the box moving than to keep it moving. return to top Answer 3 the same INCORRECT Once the box is moving it does not need the same amount of force, because the friction is less. return to top What's this question really asking? Is the force required to get the box moving is different from the force it takes to keep it moving? return to top |
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