GED Science TestPhysical ScienceHard
A student sets up an experiment with two identical carts on a frictionless track. Cart A has a mass of 2 kg and is moving at 3 m/s. Cart B has a mass of 4 kg and is initially at rest. Cart A collides with Cart B, and after the collision, the two carts stick together and move as one unit. According to the Law of Conservation of Momentum, what is the final velocity of the combined carts?
- A1.0 m/s
- B0.5 m/s
- C2.0 m/s
- D1.5 m/s
Show answer & explanationAnswer & explanation
Correct answer: A. 1.0 m/s
According to the Law of Conservation of Momentum, total momentum before collision equals total momentum after collision. Initial momentum (Cart A + Cart B) = (2 kg * 3 m/s) + (4 kg * 0 m/s) = 6 kg·m/s. After collision, the total mass is (2 kg + 4 kg) = 6 kg. So, Final momentum = (6 kg) * v_final. Setting initial = final: 6 kg·m/s = 6 kg * v_final. Therefore, v_final = 1.0 m/s.
Why the other options are wrong
- B. Incorrectly calculated momentum or mass.
- C. Possibly made an error in total mass or initial momentum.
- D. Possibly calculated (2*3)/4 or other incorrect division.
Conservation of Momentum
In a closed system, the total momentum of interacting objects remains constant, provided no external forces act on the system.
- Momentum = mass × velocity (p = mv).
- Total initial momentum = Total final momentum (Σp_initial = Σp_final).
- Applies to collisions and explosions.
- A vector quantity (direction matters).
Memory trick: Momentum's Magic: Before Equals After.