A book sliding across a smooth wooden desk gradually slows and stops. The force responsible is:
AGravity acting downward, pulling the book toward the floor
BThe normal force acting upward from the desk on the book
CAir resistance only, with no contact force at the desk surface
DKinetic friction acting opposite to the book's motion
Answer & Solution
Correct answer: D. Kinetic friction acting opposite to the book's motion
Kinetic friction between the book and the desk opposes the relative motion.
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