What is the magnitude and direction of the frictional force acting on a crate when pushed with a horizontal force of 100N and sliding at constant velocity?

When an object is sliding at constant velocity, it is in a state of dynamic equilibrium. This means that the net force acting on the object is zero.

In this scenario, a horizontal force of 100 N is being applied to the crate. For the crate to slide at constant velocity, the frictional force acting on it must balance out the applied force. Since the crate is moving, the friction involved is kinetic friction, which opposes the direction of motion. Therefore, the magnitude of the frictional force must also be 100 N, but it acts in the opposite direction to the applied force of 100 N.

This ensures that the total forces in the horizontal direction sum to zero: the 100 N applied force is balanced by a 100 N frictional force acting in the opposite direction. In this way, the crate maintains a constant velocity without accelerating.

Thus, the correct interpretation of the situation leads to the conclusion that the magnitude of the frictional force is 100 N, and its direction is indeed opposite to the direction of motion.