A uniform meter stick is balanced at the center as shown above. Which of the following shows how a .50 KG mass on a 1.0 KG mass could be hung on the meterstick so that the sticks stays balanced

Under the action of a constant force an object accelerates at 7.8 m/s2. what will the acceleration be if (a) the force is halved? (b) the object's mass is halved? (c) the force and the object's mass are both halved? (d) the force is halved and the object's mass is doubled?