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An object is sliding down an incline at a constant velocity. What must be true about the net force acting on it at that moment?
AThe net force must equal the object's full weight
BThe net force acting on it at that moment must be zero
CThe net force must point up the slope and keep growing
DThe net force must equal the normal force alone
Answer & Solution
Correct answer: B. The net force acting on it at that moment must be zero
1. A constant velocity means the acceleration is zero.
2. By Newton's second law, zero acceleration means the net force on the object is zero.
3. This happens on an incline when kinetic friction exactly balances the component of gravity along the slope.
4. The object's full weight and the normal force are each just one of the forces involved, not the net result, so neither matches a zero net force.
_Source: OpenStax College Physics (CC BY 4.0), Ch 5 "Further Applications of Newton's Laws: Friction, Drag, and Elasticity", section 5.1 Friction_
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