An object with mass of 2 kg is moving along a horizontal surface with a velocity components vx= 5m/s and vy= -2.5m/s. what is the objects speed? what is its kinetic energy?

To final the velocity, get the resultant of the given components of velocity,
                              v = sqrt ((vx)² + (vy)²)
                              v = sqrt ((5 m/s)² + (-2.5 m/s)²)
                               v = 5.59 m/s
The kinetic energy is,
                                     KE = 0.5mv²
Substituting the values,
                                    KE = 0.5(2 kg)(5.59 m/s)² = 31.2481 J