Recently, mobile manipulators are being widely employed for various service robots in human environments. Safety is the most important requirement for the operation of mobile robot in a human-populated environment. Indeed, safe human-machine interaction is one of grand challenges in robotics research. This paper proposes a novel control method to reduce impulsive compact force between a mobile manipulator and its environment by using optimized manipulator inertia and damping-based motion control. To find the optimized configuration through null space motion, the combined potential function method is proposed considering both the minimum effective mass and joint limit constraints. The results of this study show that the inertia optimization along with a damping controller significantly reduces the impulsive force upon collision and the contact force after collision.