Newton's second law with kinetic friction
A 10 kg box is pushed horizontally with 50 N across a floor with a coefficient of kinetic friction of 0.2 (g = 10 m/s²). What is the box's acceleration?
Answer B: explanation for every choice
A
This divides the friction force (20 N) by the mass.
B
Correct. Friction = μmg = 0.2 × 10 × 10 = 20 N. Net force = 50 − 20 = 30 N, so a = 30/10 = 3 m/s².
C
This ignores friction.
D
This adds friction to the applied force instead of subtracting it.
TakeawayFnet = Fapplied − μN, then a = Fnet/m.
Equations usedNewton's second lawFriction
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