Final answer:
The force you exert on the sled is equal to the force of sliding friction on its runners.
Step-by-step explanation:
In this scenario, if you are pulling a sled along a level field at constant velocity, the force you are exerting on the sled is equal to the force of sliding friction on its runners. This is known as the equilibrium condition.
When an object is moving at a constant velocity, the net force acting on it is zero. So, the force you exert on the sled must be equal to the force of sliding friction for it to maintain its constant velocity.
For example, if the force you exert on the sled is 100 Newtons, then the force of sliding friction on its runners will also be 100 Newtons in the opposite direction.