Logical Reasoning

PT143 · S3 · Q17 Rocket engines are most effective

A free, expert breakdown of this official LSAT Logical Reasoning question.

  • Save & drill this skill — build targeted practice sets from questions like this one

  • Video walkthroughs — watch every question solved step by step

  • 81 official LSATs — as questions, timed sections & full-length tests

Start practicing free

Rocket engines are most effective when exhaust gases escape from their nozzles at the same pressure as the surrounding atmosphere.

Conclusion (Thus)

To work most effectively throughout their ascents, all rockets must have both short nozzles and long nozzles on their engines.

Evidence

To work most effectively, rocket engines need their exhaust gases to be the same pressure as the surrounding atmosphere.

A short nozzle matches the pressure of low altitudes, whereas a long nozzle matches the pressure in the thin upper atmosphere.

Evaluate

Because the conclusion is conditional "to do X, it must be that Y", we might be wise to guess that LSAT is testing a missing link. Is there any new term in the conclusion?

Throughout their ascents / all rockets is new. The evidence talked about short/long nozzles and defined what it means for a rocket to work most effectively.

You need a short nozzle for low altitudes and a long nozzle for the thin upper atmosphere. So I guess the author is assuming that

If we were trying to use an Objection mindset, we'd be thinking,

Maybe some rockets only ascend to low altitudes, so they could get away with just having short nozzles. Maybe some rockets only "turn on" once they reach the thin upper atmosphere, so they could get by with just long nozzles.

Goal

Look for an answer dealing with the new Conclusion language (throughout their ascents, all rockets) establishing that we will be dealing with both low altitudes and the thin upper atmosphere, or look for an answer ruling out an objection like the ones we made.

17.

Which one of the following is an assumption the argument requires?

  1. Equipping a rocket's engines with

    Irrelevant Comparison: more difficult

    The author's argument has nothing to do with which nozzle setup would be easier or harder to install. It is purely about which nozzle setup would be required if your goal were "working most effectively throughout the ascent". If we negated this answer and said, "Hey author, it is significantly more difficult to equip a rocket with both short and long", that doesn't weaken the conclusion at all. He isn't saying short + long is feasible, affordable, easy, etc. He's only saying it's required if you wanted a rocket to work most effectively throughout the ascent.

    2% picked this

  2. Correct

    At some point during their

    Why this is right

    This has the new language from the conclusion (during their ascent, all rockets). Since the author thinks that all rockets need a long nozzle (which is only needed for working most effectively in the upper atmosphere), that must mean that the author is assuming that all rockets go through the thin upper atmosphere during their ascent. If we negated this answer, it would turn into an objection: Hey, author, not all rockets pass through the upper atmosphere during their ascent. Some of them stay at low altitudes, so they only need a short nozzle to work most effectively.

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

    64% picked this

  3. A rocket with only short

    Too Strong: cannot reach

    The author was never saying that you need a long nozzle to reach the upper atmosphere, only that you would need it for your rocket to work most effectively in the upper atmosphere.

    3% picked this

  4. For a rocket to work

    Too Strong: to work effectively

    The argument established that for a rocket to work most effectively, the exhaust gases should match the pressure of the surrounding atmosphere. This answer is going way farther than that, saying that for a rocket to work effectively at all, they exhaust gas must match the pressure of the surrounding atmosphere. When we say stuff like, "for this zinc lozenge to work most effectively, you shouldn't eat any citrus foods within 30 minutes of taking it", we're not saying, "If you do eat citrus foods within 30 minutes, it isn't effective at all." We're just saying, "it's less effective".

    15% picked this

  5. For a rocket to work

    Too Specific: one engine has both

    Although this sounds like a tempting inference we could draw from the paragraph, it gets too specific. If a rocket had four engines, two of them with short nozzles and two of them with long nozzles, then it could use the short nozzle engines at low altitudes and the long nozzle engines at high altitudes. Why does it need to have at least one engine that has both nozzles? (Is it even possible for a single engine to have more than one nozzle on it?) The specificity of this answer is what we want to chase us away. The conclusion is just saying, "all rockets need both short and long nozzles on their engines", but it never specifies that they need a short and long on the same engine.

    15% picked this

Continue the review in LSAT Lab

Save this question, watch the video walkthrough, and drill similar questions in your LSAT Lab account.

Save and practice this skill
LSAT Lab

Turn this review into a targeted study plan.

Save this question, drill more like it, watch the video walkthrough, and track your progress in your LSAT Lab account.

Start practicing free