Why does the cyclist accelerate as he coasts downhill?

A.
The force of friction propels the cyclist and the bicycle down the hill.

B.
The force of the cyclist and the force of the bicycle added together increase the downhill acceleration.

C.
The mass of the cyclist opposes the mass of the bicycle, causing it to accelerate downhill.

D.
The unbalanced force of gravity acts on the mass of his body and the bicycle.

Question

Why does the cyclist accelerate as he coasts downhill?
	
	
 
A.
	The force of friction propels the cyclist and the bicycle down the hill.
	
 
B.
	The force of the cyclist and the force of the bicycle added together increase the downhill acceleration.
	
 
C.
	The mass of the cyclist opposes the mass of the bicycle, causing it to accelerate downhill.
	
 
D.
	The unbalanced force of gravity acts on the mass of his body and the bicycle.

anonymous · Answer

Friction works against the direction of motion.  The mass of the cyclist doesn't oppose the mass of the bike.  You're left with B or D.   Since nothing is balancing the force of gravity, that is the source of the acceleration.