Question

In a lab experiment, a student is trying to apply the conservation of momentum. Two identical balls, each with a mass of 1.0 kg, roll toward each other and collide. The velocity is measured before and after each collision. The collected data is shown below.

A 5 column table with 3 rows. The first column is unlabeled with entries Trial 1, Trial 2, Trial 3, Trial 4. The second column is labeled Initial Velocity Ball A (meters per second) with entries positive 1, positive 0.5, positive 2, positive 0.5. The third column is labeled Initial Velocity Ball B (meters per second) with entries negative 2, negative 1.5, positive 1, negative 1. The third column is labeled Final Velocity Ball A (meters per second) with entries negative 2, negative 0.5, positive 1, positive 1.5. The fourth column is labeled Final Velocity Ball B (meters per second) with entries negative 1, negative 0.5, negative 2, negative 1.5.

Which trial shows the conservation of momentum in a closed system?

Trial 1
Trial 2
Trial 3
Trial 4

Answer 1

Trial 2.

Calculation (m = 1.0 kg so p = v1 + v2):

- Trial 1: p_i = 1 + (−2) = −1; p_f = (−2) + (−1) = −3 → not conserved
- Trial 2: p_i = 0.5 + (−1.5) = −1.0; p_f = (−0.5) + (−0.5) = −1.0 → conserved
- Trial 3: p_i = 2 + 1 = 3; p_f = 1 + (−2) = −1 → not conserved
- Trial 4: p_i = 0.5 + (−1) = −0.5; p_f = 1.5 + (−1.5) = 0 → not conserved

Only Trial 2 satisfies momentum conservation.