Determining motion from average speeds in intervals

Steps:

• Compute average speeds: 10m/2s=5 m/s (0-2s), 10m/2s=5 m/s (2-4s), 11m/2s=5.5 m/s (4-6s), 13m/2s=6.5 m/s (6-8s), 16m/2s=8 m/s (8-10s), 23m/2s=11.5 m/s (10-12s).
• From 0-4s, speeds are constant at 5 m/s, indicating constant speed.
• From 4-12s, speeds increase (5.5, 6.5, 8, 11.5 m/s), showing acceleration.
• Speed increments (0.5, 1.0, 1.5, 3.5 m/s) vary, confirming non-uniform acceleration.

Why A is correct:

• Equal distances in 0-4s intervals mean constant speed (distance = speed × time, with fixed time); unequal, increasing speed changes after 4s indicate non-uniform acceleration per kinematics definitions.

Why the others are wrong:

• B: Speed increments are unequal, not linear as required for uniform acceleration.
• C: Distances of 10m in 0-4s intervals mean motion, not rest (distance > 0).
• D: Not at rest in 0-4s, and acceleration is non-uniform.

Final answer: A