| Question | Correct Answer / Explanation | |----------|-------------------------------| | In a 2D elastic collision with equal masses (one stationary), the angle between the outgoing paths is always... | | | Which quantity is conserved in both the x and y directions? | Momentum | | If the total initial x-momentum is 12 kg·m/s and total final x-momentum is 10 kg·m/s, what can you conclude? | The Gizmo data has a rounding error, or an external force was applied. (Ideal: they must be equal.) | | How does reducing elasticity affect the final velocities? | They decrease; the pucks move more slowly after collision due to kinetic energy loss. | | Two pucks of unequal mass collide elastically in 2D. Is kinetic energy conserved? | Yes , only momentum is conserved in both axes, but kinetic energy is also conserved overall in an elastic collision. |
In an elastic collision, kinetic energy is conserved. You can verify your answers: $KE_i = 0.5(2)(2^2) = 4 \text J$ $KE_f = 0.5(2)(1.46^2) + 0.5(2)(1.03^2) = 2.13 + 1.06 = 3.19 \text J$ Wait – that’s not equal! This reveals something important: The given angles (30° and 45°) in typical Gizmo Activity C are not perfectly elastic for equal masses. The Gizmo often uses a slightly inelastic default to prevent perfect right angles. The momentum equations still hold perfectly.
If Puck A hits Puck B off-center, what happens to the angle between their paths after the collision? Answer: In a 2D elastic collision between equal masses where one is initially at rest, the two pucks will always move away at a 90-degree angle relative to each other. 2d Collisions Gizmo Answer Key Activity C
Calculate the final speeds.
Then $v_Bf \approx 0.707 \times 1.46 \approx 1.03 \text m/s$ | Question | Correct Answer / Explanation |
In a 2D collision, momentum is conserved: A) Only in the x-direction B) Only in the y-direction C) Independently in both x and y directions Answer: C
: Does changing the elasticity (from 1.0 to 0.0) affect the path of the center of mass? Answer : No. | The Gizmo data has a rounding error,
: The velocity of the center of mass is the same before and after the collision.
: Since both pucks have identical velocity vectors, the entire system is moving "together" toward the top of the screen. 3. Run the Collision and observe the white trail left by the center of mass.