A box is already sliding across a rough floor. The person pushing it pushes harder. What happens to the magnitude of the kinetic friction?
AIt rises steadily
BIt falls to zero
CIt doubles at once
DIt stays the same
Answer & Solution
Correct answer: D. It stays the same
1. Once the box is moving, the friction acting on it is kinetic friction.
2. For kinetic friction the value remains the same regardless of the magnitude of the applied force.
3. Only the normal force and the surfaces themselves change the size of kinetic friction.
4. Pushing harder therefore gives a bigger resultant force and more acceleration, not more friction.
_Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 2: Newton's laws_
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