Two carts with masses 10.0kg and 2.5 kg move in opposite directions on a frictionless horizontal track with speeds of 6.0m/s and 3.0 m/a respectively. The carts stick together after colliding head on. Find the final speed. Please help!!

Diego is trying to lift a piano to the second floor of his house. diego uses a pulley system and gives a big lift to the piano.the piano moves upward, then stops, and then it starts to fall to the ground. which list best describes the forces on the piano in the proper order? positive force → balanced force → negative force negative force → balanced force → positive force positive force → unbalanced force → negative force negative force → unbalanced force → positive force