Question

a skateboarder rides down the street. when his feet push down on the skateboard, what is the reaction force?
a. the skateboard pushes up on his feet.
b. the skateboard pushes down on the ground.
c. earths gravity pulls down on his feet.
d. earths gravity pulls down on the skateboard.

Explanation:

According to Newton's third law of motion, for every action, there is an equal and opposite reaction. When the skateboarder's feet push down on the skateboard (action force), the skateboard exerts an equal and opposite force (reaction force) on the feet.

Answer:

A. The skateboard pushes up on his feet.