The force acting on the object is constant, so the acceleration of the object is also constant. By definition of average acceleration, this acceleration was
a = ∆v / ∆t = (6 m/s - 0) / (1.7 s) ≈ 3.52941 m/s²
By Newton's second law, the magnitude of the force F is proportional to the acceleration a according to
F = m a
where m is the object's mass. Solving for m gives
m = F / a = (10 N) / (3.52941 m/s²) ≈ 2.8 kg