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Rocket engines are most effective when exhaust gases escape from their

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Rocket engines are most effective when exhaust gases escape from their  [#permalink]

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New post 16 Aug 2018, 03:31
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Rocket engines are most effective when exhaust gases escape from their nozzles at the same pressure as the surrounding atmosphere. At low altitudes, where atmospheric pressure is high, this effect is best produced by a short nozzle, but when the rocket passes through the thin upper atmosphere, a long nozzle becomes more effective. Thus, to work most effectively throughout their ascents, all rockets must have both short nozzles and long nozzles on their engines.

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

A) Equipping a rocket's engines with both short and long nozzles is not significantly more difficult than equipping them with nozzles of equal lengths.

B) At some point during their ascents, all rockets will pass through the thin upper atmosphere.

C) A rocket with only short nozzles on its engines cannot reach high altitudes.

D) For a rocket to work effectively, its engines' exhaust gases must leave the nozzles at the same pressure as the surrounding atmosphere throughout the rocket's ascent.

E) For a rocket to work most effectively at both low and high atmospheric pressures, it must have at least one engine that has both a short nozzle and a long nozzle.

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Re: Rocket engines are most effective when exhaust gases escape from their  [#permalink]

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New post 16 Aug 2018, 04:56
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[quote="manasveek"]Rocket engines are most effective when exhaust gases escape from their nozzles at the same pressure as the surrounding atmosphere. At low altitudes, where atmospheric pressure is high, this effect is best produced by a short nozzle, but when the rocket passes through the thin upper atmosphere, a long nozzle becomes more effective. Thus, to work most effectively throughout their ascents, all rockets must have both short nozzles and long nozzles on their engines.

The short nozzle is for the atmosphere on Earth and the long nozzle for the thin upper atmosphere. All the rockets to be fitted with both of them means there is a requirement of both nozzles and that would occur only when the rocket has to cross the upper atmosphere too.- clearly this is the Assumption too

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

A) Equipping a rocket's engines with both short and long nozzles is not significantly more difficult than equipping them with nozzles of equal lengths.
we require nozzles of both types and difficulty is not being talked of.

B) At some point during their ascents, all rockets will pass through the thin upper atmosphere.
Correct


C) A rocket with only short nozzles on its engines cannot reach high altitudes.
More efficient is the word and not that the short nozzle cannot cross upper atmosphere

D) For a rocket to work effectively, its engines' exhaust gases must leave the nozzles at the same pressure as the surrounding atmosphere throughout the rocket's ascent.
This is already given in para

E) For a rocket to work most effectively at both low and high atmospheric pressures, it must have at least one engine that has both a short nozzle and a long nozzle.
again cannot be an assumption

B
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Re: Rocket engines are most effective when exhaust gases escape from their  [#permalink]

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New post 16 Aug 2018, 06:01
Wonderfully explained by chetan2u

Further, try to negate option (B)

Quote:
At some point during their ascents, some rockets will pass through the thin upper atmosphere
Here the conclusion falls apart, hence answer must be (B)
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Re: Rocket engines are most effective when exhaust gases escape from their &nbs [#permalink] 16 Aug 2018, 06:01
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