Newton's Third Law in Bicycle Drive Train

Steps:

• Cyclist pushes backward on pedals, applying torque to front sprocket.
• Front sprocket rotates, pulling chain backward and creating tension.
• Tension transmits through chain, causing it to push forward on rear sprocket.
• This forward push on back wheel equals magnitude of pedal force, opposite in direction via chain interactions.

Why B is correct:

• Newton's third law requires equal and opposite forces between interacting objects; the backward pedal force on the sprocket-chain system reacts as the chain's forward force on the back wheel.

Why the others are wrong:

• A: Road exerts forward static friction on wheel to propel bike, not backward; it's external, unrelated to pedal-chain pair.
• C: Chain tension is internal magnitude, not the directional push force on the wheel.
• D: Air resistance and friction balance propulsion for constant speed but are drag forces, not reaction to pedal push.

Final answer: B