Impulse examples

A hose sprays water directly at a wall. If the volume of water emerging from the hose is X liters/second, and the water has velocity v, directed horizontally, how much force is exerted on the wall by the water?

Assume that the water does not bounce back, but is simply stopped by the wall. Focus on one second worth of water. X liters has a mass of X kg, so the momentum of the water goes from Xv to zero, a change of -Xv. To produce this change in momentum, the wall must exert a force on the water of -Xv newtons. The water exerts an equal and opposite force on the wall, Xv newtons in the direction the hose points.

If v = 10 m/s and X is 3 liters/second, the force has a magnitude of 30 N.

A mass moving in the x direction at constant speed on a frictionless table is subjected to a force in the y-direction. The force is applied for 0.5 seconds starting at t=2 seconds. Which of the following situations corresponds to the motion of the mass?