Question

Other than the applied force Usain is using to propel himself forward, what other forces do you think are acting on him during his race? Draw a free-body diagram of Usain during the race, and justify why you think each force you listed is acting on him. Are these forces helping Usain, hindering Usain, or having no effect on his race?

Answer 1

Step-by-step explanation

Since Usain is running on a surface, there are two more forces acting on him: the normal force, upward, perpendicular to the surface, and his weight, downward - assuming he is running on a horizontal surface.

There is one more force that is acting on him, and that is air resistance. This force is opposite to Usain's motion, so it is hindering Usain.

To draw the free body diagram, we have to draw the 4 forces mentioned above. Let's assume Usain is running to the left, so the force he uses to propel himself forward is to the right. Then air resistance is opposite to his motion, so it is a leftward force. Finally, the two vertical forces - that have no effect on his race rather than keeping him on the ground, are the normal force and the weight.