A rough, inclined plane has a string attached to it at the point C. The string has natural length 1.4m and modulus of elasticity 80N. The string is then attached to a particle, P, of mass 4 kg. P is farther down the plane than C. The particle P is then pulled down the plane so that it is 4 m from C and released. Given that the coefficient of friction between the particle and the plane is 0.5, and the plane has a 10° incline, find the speed of the particle as it reaches the point C for the first time.