PT157 S2 Q7 ExplanationThe mu mesons generated by

Answer choices, explained

1. A

   Opposite (if anything)5% picked this

   take longer to reach Earth than

   The evidence does not support the idea that mu mesons take longer to reach Earth than expected. The problem the stimulus presents is not about travel time — it is about survival time. We detect far more atmospheric mu mesons than the lab decay rate predicts, meaning they survive longer than expected, not that they travel slower. If they took longer to reach Earth, we would expect to detect even fewer, not more. This answer moves in the wrong direction.

   5%
2. B

   Out of Scope: difficult7% picked this

   are quite difficult to detect with

   The stimulus is about the number of mu mesons we detect relative to expectations, not about the difficulty of detection. The evidence discusses decay rates, travel speeds, and detection counts. Whether mu mesons are easy or hard to detect with available equipment is a completely separate issue. Even if detection were difficult, that would not explain why we detect more mu mesons than the lab-based predictions indicate — difficulty would suggest fewer detections, not more.

   7%
3. C

   Opposite (if anything)9% picked this

   are much less numerous than previously

   This answer suggests there are fewer atmospheric mu mesons than previously thought. But the puzzle is that we detect far more than predicted by lab-based decay rates. If mu mesons were less numerous, that would make the detection surplus even more surprising — we detect 100 times what decay rates predict, and there are even fewer of them to begin with? That deepens the mystery rather than resolving it. Additionally, the evidence is about decay rates and speed, not about how many mu mesons are generated. The conclusion should address why mu mesons survive longer at high speed.

   9%
4. D

   Correct76% picked this

   decay more slowly than mu mesons almost

   Why this is right

   This is the conclusion the evidence supports. Atmospheric mu mesons travel near the speed of light and are detected in far greater numbers than lab-based decay rates predict. Lab mu mesons are nearly at rest and decay quickly. The only way to reconcile the detection data with the decay data is to conclude that mu mesons moving at high speed decay more slowly than those at rest. The contrapositive confirms this: if atmospheric mu mesons decayed as fast as lab ones, we would detect only 1/100 of the actual number. Since we detect far more, they must not decay as fast. The distinguishing variable between the two groups is speed, so the conclusion links high speed to slower decay.

   Skill tested: Most Supported · how this choice captures the argument's function is the move to repeat next time.

   76%
5. E

   Contradicted2% picked this

   are probably not generated by cosmic

   The very first sentence of the stimulus states that mu mesons are "generated by cosmic rays just outside Earth's atmosphere." Nothing in the subsequent evidence undermines this statement. The information about decay rates and detection counts has no bearing on how mu mesons are generated — it only addresses how quickly they decay at different speeds. This answer contradicts an explicit premise without any supporting evidence.

   2%