If a crate is pushed with a force of 100N and experiences friction of 70N over 10 m, how much kinetic energy does it gain?

To determine the kinetic energy gained by the crate, we need to assess the net force acting on it and the work done by that net force over the distance of 10 meters.

Initially, the crate is pushed with a force of 100 N. However, it experiences a frictional force of 70 N that opposes the motion. The net force can be calculated by subtracting the frictional force from the applied force:

Net force = Applied force - Frictional force Net force = 100 N - 70 N = 30 N

The work done by this net force can be found using the formula for work, which is:

Work = Net force × Distance

Substituting the values we have:

Work = 30 N × 10 m = 300 J

This work done by the net force results in a gain in kinetic energy. Therefore, the crate gains 300 Joules of kinetic energy as it is pushed over the distance of 10 meters against the frictional force.

Thus, the correct answer is that the crate gains 300 J of kinetic energy.