An object moving along the \(x\)-axis experiences a constant force in its direction of motion, \(F_{x}=56 \mathrm{~N}\). At \(t=1.2 \mathrm{~s}\), the object is moving at \(2.0 \mathrm{~m} / \mathrm{s}\) and at \(t=3.5 \mathrm{~s}\) it is moving at \(2.8 \mathrm{~m} / \mathrm{s}\). What is the inertia of the object?