I believe if the force is less than the weight of the ruler then the ruler wouldn't spin. It would rotate clockwise then counter-clockwise back to the resting position.
Homework Statement
A horizontal stream of water from a fire-fighter's hose hits a vertical wall. The firefighter knows that 16.9 kg of water are emitted from the hose per second, and that the water has a speed of 45.5 m/s. At the instant when it hits the wall, the direction of the velocity...