spring force

[Deepa100]

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Suppose the pilot chair in a supersonic jet is constructed with a single large spring in its back to support the pilot. As the pilot lands his jet, he brings it from supersonic speed to rest at a constant acceleration, the force exerted by the spring is:
a)inversely proportional to the mass of the pilot.
b)inversely proportional to the constant of the spring.
c)directly proportional to the time it takes to bring the jet to rest.
d)directly proportional to the original velocity of the jet.

Answer: D, why?

 

[BerkReviewTeach]

Suppose the pilot chair in a supersonic jet is constructed with a single large spring in its back to support the pilot. As the pilot lands his jet, he brings it from supersonic speed to rest at a constant acceleration, the force exerted by the spring is:
a)inversely proportional to the mass of the pilot.
b)inversely proportional to the constant of the spring.
c)directly proportional to the time it takes to bring the jet to rest.
d)directly proportional to the original velocity of the jet.

Answer: D, why?

Don't you have a detailed explanation with that question? There's a good deal of information in each of the answer choices, so whatever the soruce is, they surely have a good review as to why A and B are out (based on the equation) and why C is out (a is inversely proportional to deltaT). The explanation as to why D is right surely mentioned that a is directly proportional to deltaV, so that is the best, although not perfect, answer.

 

[silverlion]

Hey Deepa...

Where are you getting these questions from? I had a look at the question and I didn't come to a quick conclusion either but the method of elimination just leaves D as the best possible answer.

We know that the equation for the force exerted by a spring is
F= -k (delta x)^2

Where delta x is the change in length of the spring.

Therefore B gets eliminated right away. If you think about it A and C get eliminated intuitively as well...

If you think about it. The force of the spring described by the equation is the force that it can exert. Which means that it could be equated with m*a.

SO, F= -k *(delta x)^2 = m*a

So the force is directly proportional to the mass of the pilot. A is out

Acceleration is change in velocity/ change in time.
so a is indirectly proportional to the time.... C is out...

That leaves D....

 

[Deepa100]

Hey Deepa...

Where are you getting these questions from? I had a look at the question and I didn't come to a quick conclusion either but the method of elimination just leaves D as the best possible answer.

We know that the equation for the force exerted by a spring is
F= -k (delta x)^2

Where delta x is the change in length of the spring.

Therefore B gets eliminated right away. If you think about it A and C get eliminated intuitively as well...

If you think about it. The force of the spring described by the equation is the force that it can exert. Which means that it could be equated with m*a.

SO, F= -k *(delta x)^2 = m*a

So the force is directly proportional to the mass of the pilot. A is out

Acceleration is change in velocity/ change in time.
so a is indirectly proportional to the time.... C is out...

That leaves D....

It's Q from the kaplan material. I did read their explanation but I did not understand it very well so wanted to see what people thought about this. Your explanation is more simple which is what I like.
Thx!