The thrust required for a rocket to gain altitude is proportional to

Question

The thrust required for a rocket to gain altitude is proportional to its mass, and the ability of a rocket to provide thrust is proportional to the rate at which its engines can convert their fuel to energy. This is why small solid-fuel rockets gain altitude and reach escape velocity much more quickly than do huge combination-fuel vehicles like NASA’s space shuttle, which must labor tremendously to exit the earth’s atmosphere.

The explanation above depends on the validity of which one of the following assumptions?

A. The amount of thrust required to gain altitude is no greater for huge space vehicles than it is for small solid-fuel rockets.
B. Small solid-fuel rockets can move more quickly than huge combination-fuel space vehicles.
C. The ratio of mass to rate of energy conversion is smaller in small solid-fuel vehicles than it is in huge combination-fuel space vehicles.
D. There is relatively little variation in the ability of combination-fuel rockets to provide thrust.
E. The amount of thrust required by a rocket to achieve escape velocity is proportional to the mass of the fuel it carries.

Raisakatyal · Answer

Didn't really understand why option C is the correct answer here.

Mukulkumar19 · Answer

A. The amount of thrust required to gain altitude is no greater for huge space vehicles than it is for small solid-fuel rockets.
  This actually undermines the fact given in the first sentence of the argument  
B. Small solid-fuel rockets can move more quickly than huge combination-fuel space vehicles.
 Doesnt provide any assumption, as the same is mentioned in the argument. 
C. The ratio of mass to rate of energy conversion is smaller in small solid-fuel vehicles than it is in huge combination-fuel space vehicles.
 Argument tells us that Mass(M) is proportional to thrust required, means greater the M more the thrust required, also thrust is proportional to Rate of Energy conversion(Re), means greater Re more the thrust. Ok so we know that smaller rockets have less mass and larger rockets have more mass. This answer statement states that M/Re is less for smaller rocket which clearly means that smaller rocket have less M and greater Re in comparison to larger rocket and hence travels faster.  
D. There is relatively little variation in the ability of combination-fuel rockets to provide thrust.
 Little variation??? in comparison to what 
E. The amount of thrust required by a rocket to achieve escape velocity is proportional to the mass of the fuel it carries.
 not only mass of fuel but mass of whole rocket

Hope I made some sense.

sayan640 · Answer

MartyMurray   KarishmaB  Can you please discuss this question ?

Posted from my mobile device

Vaishbab · Answer

MartyMurray   KarishmaB  can you help with this one? I must have missed something while learning the concepts. Option C corroborates with what's mentioned in the stem - that small solid fuel vehicles have lower mass and higher rate of energy conversion. That naturally means that the mass/rate ratio should be lower for solid fuel rockets. But why would it be the right answer?

KarishmaB · Answer

The argument does not mention that small rockets have lower mass and higher rate of energy conversion. 
The argument only mentions that thrust needed to gain altitude is proportional to mass and thrust produced is proportional to rate of energy conversion. 
This is given as the reason by the author why small rockets gain altitude quickly.

To say that this is the reason small rockets gain altitude quicker, the author is assuming that small rockets have a lower ratio of mass to rate of energy conversion. That is why (C) is the answer. Note carefully exactly what is given. This is the reason assumption questions are challenging at times - we think that the assumption is already given but "given" means "written in words," not assumed.

utkarshs2402 · Answer

Doubt here:
If I negate B: "Small solid-fuel rockets CAN NOT move more quickly than huge combination-fuel space vehicles", won't this break the conclusion that small solid-fuel rockets reach gain altitude and reach escape velocity faster than huge combination-fuel space vehicles?

MartyMurray   KarishmaB

The thrust required for a rocket to gain altitude is proportional to

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The thrust required for a rocket to gain altitude is proportional to

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