Recall the portion of the video in which the girl pushes her brother on the sled at constant velocity. The pushing force she exerts on the sled is the frictional force the ground exerts on the sled.

The pushing force she exerts on the sled is equal to the frictional force the ground exerts on the sled.

Explanation:

We have given that the brother of the girl is moving with a constant velocity. It means that the acceleration will be zero. Hence, the net force would be zero.

If the net force is zero, then the pushing force exerted on the sled will be equal to the frictional force that ground exerts to the sled.

So, both forces will be equal.

this is poiselle's equation from fluid mechanic in physics. mech eng

energy can be converted from one form to another, but it cannot be created or destroyed in ordinary chemical or physical means. do not understand what you are asking but hope this