Kaplan Physics Practice Question

[betterfuture]

A consumer is comparing two new cars. Car A exerts 250 horsepower, while Car B exerts 300 horsepower. The consumer is most concerned about the peak velocity that the car can reach. Which of the following statements would best inform the consumer's decision? Note: 1 horsepower=745.7 W

Answer: Car A and Car B both have unlimited velocities, ignoring nonconservative forces.

Can someone who is really good with physics clue me in on what this question is asking and how they got the answer?

And also, would it be silly to go over such questions as these for the MCAT, cause I doubt the MCAT would ever bring such a question/ Just asking because I am having a hard time with this topic. Thank you.

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[theonlytycrane]

disclaimer: I'm not great at physics!

Here's how I process the information: All that is given is horsepower for each car and a conversion from horsepower to Watts. The unit (Watts) makes me think of the equation Power = Work / t with the units of Watts. Work is force * distance in the direction of travel and I'm imagining the cars traveling along a straight path in the direction of the driving force from the engine. Given this, Car B has more force per unit time than Car A so it will accelerate faster.

With that said, the question says that the consumer is most concerned about peak velocity. If the consumer was concerned about reaching a target speed in the fastest amount of time- then this would describing Car B. But given unlimited time, both cars will reach an "unlimited" velocity as they will continue to accelerate in the direction of travel. This wouldn't happen in reality as there are mechanical limitations for a car engine and the real world does have many non-conservative forces to consider.

Hope this helps! (I hope the consumer goes with the Nissan 370Z)

 

[betterfuture]

Wait. How did you figure out that Car B would reach a target speed in the fastest amount of time?

 

[theonlytycrane]

Car B has more horsepower than Car A -> so it also has more power.

power = work / t and work = force * distance in the direction of travel.

Given the same distance traveled and time, Car B will experience more force than Car A. Force = ma so it will accelerate faster and reach a higher speed in some fixed amount of time. So if the goal was to reach a specific target speed, Car B would reach it before Car A.

 

[betterfuture]

So because it has more F, couldn't it also mean that it could have a bigger mass as well as having higher acceleration? Though, I don't know what having a bigger mass would necessarily tell us anything for this problem.

 

[theonlytycrane]

So because it has more F, couldn't it also mean that it could have a bigger mass as well as having higher acceleration? Though, I don't know what having a bigger mass would necessarily tell us anything for this problem.

Without knowing the masses of the two cars, this is also possible. I guess acceleration for the two cars could also be the same such that they reach a target speed at the same time. The heavier car would just use more power (do more work) to do so.

 

[betterfuture]

Would it be safe to say that these type of questions wouldn't be "high yield" per say on the MCAT, because I doubt comparing car speeds and their power would somehow be important in a heavily biomedical/biological tested MCAT.

 

[theonlytycrane]

Would it be safe to say that these type of questions wouldn't be "high yield" per say on the MCAT, because I doubt comparing car speeds and their power would somehow be important in a heavily biomedical/biological tested MCAT.

Likely not- but practicing your approach to using prior knowledge and equations to make sense of new situations is what is most important.

 

[betterfuture]

Thanks!