A mass of 5.0 kg is attached to one end of a spring with a spring constant 80 N/m. The other end is attached to a rigid wall. The spring is initially at rest in its equilibrium position, then a force of 100 N pulls the mass away from the wall, stretching the spring. The coefficient of friction between the mass and the floor is 0.30. What is the speed if the box after it has moved 0.50 m?