Q7 - Inertia affects the flow of water

[ManhattanPrepLSAT1]

Question Type
Most Supported

Stimulus
When water is pumped through a closed system of pipes, inertia has two effects: first, when the pump is switched on, the water takes time to achieve full speed; and second, when the pump is switched off, the decrease in water flow is gradual. The effects of inertia on water pumped through a closed system of pipes is similar to the effects of inductance in electrical circuits.

Anticipate
The analogous effects of inertia on water pipes and inductance on electrical circuits suggests that we should anticipate one of the affects of inertia on water pipes applied to inductance on electrical circuits.

Correct Answer
(A) applies the discussion of how inertia affects the flow of water in a system of pipes to the influence of inductance on electrical circuits. And most importantly, it does so without overstating the relationship.

Incorrect Answers
(B) is too strong. The statements say that inertia affects the flow of electrical current in closed circuits, not that inertia is required.

(C) provides an explanation for why inductance of electrical flows is similar to the flow of water in a closed system of pipes. However, this goes further than the statements actually suggest.

(D) is out of scope. The statements do not address the goals of electrical engineers.

(E) is too strong. We know that the affect of inductance on electrical circuits is similar to inertia on water pumped through a system of pipes, and that inertia has the effect of slowing the water down gradually when a pump is switched off, but we cannot say inductance will cause an electrical signal to continue for a second or two once it has been switched off.

#officialexplanation

[LSAT-Chang]

Could someone help me with this question? I thought it was a bit confusing... I picked E just because I was down to A and E and wasn't sure if we could infer A...

[americano1990]

(E) is wrong for two reasons.

First, although we know that once we turn off the pump, the water would slow down gradually, where in the stimulus can we get any idea about the specific values of "a second or two"?

Plus, the active voice in (E) is also the problem. It says that when the pump is switched off, IT continues to pump. However, the pump is turned off, so its not the one thats pumping. Its just the water that is flowing by itself, slowing down on its way.

But (A) on the other hand is clearly the winner. You already know the function of inertia in the water pump, which influences the starting and ending speed of water. And we are told in the end that induction serves analogous function in circuits. Put it in GRE/old SAT format, its inertia:water pump=inductance: circuit.

Does this help?

[aescano209]

Hello,

I just wanted to post up a quick anaylsis of this question for future readers. So our goal here is to find an answer choice that is most strongly supported from the stimulus. Keep in mind that it doesn't have to be 100% true, but can be supported by what is provided in the stimulus. Given that let's break down the core.

We are given basically a bunch of facts about inertia, water flow, inductance, and electrical circuits.
Premise 1: inertia affects flow of water in pipes
Premise 2: First on takes time to reach full speed water flow
Premise 3: When turned off, it takes time for it to decrease water flow.
Premise 4: Inductance in electrical circuit are similar to inertia and water flow.

A thing to note with the multiple facts given is that with the last premise you have to notice that the author/writer here isn't saying the two are connected with each other, but really that he uses inertia and flow as an analogy to describe a similar process with inductance and electrical circuits. To connect the two in some way would not necessarily be deductible unless we are given some other premise that connects the two, which we are not given. With that and a grasp of the facts, let's approach the answer choices.

(A) is correct. If the inductance is like inertia, and elecrical currents are like water flow, we can deduce that the inductance affects the water flow. Remember the two are analagous in the way they operate.
(B) is wrong because we don't know the circuit requires inertia. We know inductance affects ciruit flow, but we cannot infer that the two are related.
(C) is wrong again tries to connect two analagous situations which cannot be inferred.
(D) is wrong because electrical engineers are out of scope. We don't know anything about electrical engineer and what they are trying to do.
(E) is wrong because we know its a gradual decrease, but we don't know the extent of time it takes to decrease. Maybe it's a second or two or maye its 24 hrs. We can't infer that so eliminate.

[tommywallach]

Thanks so much, Aescano!