LSAT 156 | Section 2 | Logical Reasoning: Q25

LR Question 25 Explanation

QUESTION TEXT: According to the Newtonian theory of gravity …

QUESTION TYPE: Sufficient Assumption

CONCLUSION: You don’t need to know what the Sun and planets are made of to calculate their orbit.

REASONING: Gravity depends only on mass and distance, not composition.

ANALYSIS: I’m certainly not a rocket scientist, astronomer, or anything of that sort. What does gravity have to do with calculating orbits?

There’s a jump there. This argument only works if calculating orbits depends only on gravitational force. Otherwise, even if gravity ignores composition, something else involved in orbit calculation might still require knowing what the bodies are made of.

So the missing step is: orbit calculations rely only on gravitational forces. Once you add that, the reasoning works: gravity doesn’t depend on composition, and orbits depend only on gravity, so composition is irrelevant.

Maybe it doesn’t take a rocket scientist to figure it out!

___________

1. This reverses the relationship and isn’t needed. The argument is about what gravity depends on, not what mass depends on.
2. CORRECT. This connects gravitational force to orbit calculation, making the conclusion follow.
3. We’re not supposed to undermine the Newtonian theory.
4. This is about determining mass, not whether composition is needed for orbit calculation.
5. This adds a relationship between force and distance but doesn’t address whether composition matters for calculating orbits.