Answer: the friction acting on the moving body.
- A the friction acting on the moving body
- B the total mass of the moving body
- C the weight of the body itself
- D the geometric shape of the body
Correct answer: A. the friction acting on the moving body
Explanation: A moving body slows and stops because of friction and air resistance. On a perfectly frictionless surface no force is needed to keep it moving, which is exactly Newton's first law.
Free-body diagram of a block on an incline: weight (mg) resolves into mg sinθ along the slope and mg cosθ into the slope, balanced by the normal force N and friction f.
Concept context
Newton's three laws, friction, circular motion, and free body diagrams.