# Practice Exam Difficulty



## cornsnicker3 (Mar 5, 2018)

If the SlaythePE practice exam is royaling beating me up, this more indicative of my lack of preparedness or the difficulty of the practice exam?


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## cornsnicker3 (Mar 5, 2018)

cornsnicker3 said:


> If the SlaythePE practice exam is royaling beating me up, this more indicative of my lack of preparedness or the difficulty of the practice exam?


*is this...


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## Slay the P.E. (Mar 5, 2018)

cornsnicker3 said:


> If the SlaythePE practice exam is royaling beating me up, this more indicative of my lack of preparedness or the difficulty of the practice exam?


Cornsnicker3:

Our intent was to make it a little bit harder than the NCEES practice exam, but still not too hard so that the problems were absurdly long or complicated, which we thought would not be valuable.
 
However, the feedback we’ve received in private from our customers as well as in public via EngineerBoards from people who took it last October is that our exam is very close in difficulty and style to the actual exam. 
 
We hope that was helpful. 
 
Needless to say we are looking forward to the opinions of other forum members here.
 
Best,


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## Sheshtawy (Mar 6, 2018)

cornsnicker3 said:


> If the SlaythePE practice exam is royaling beating me up, this more indicative of my lack of preparedness or the difficulty of the practice exam?


Probably lack of preparedness. But it's alright, you still have plenty of time to revisit the sections you're struggling with. The practice exam is very close in difficulty to the actual exam, except for a couple of heat exchanger problems which were just a bit too much.


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## Vel2018 (Mar 6, 2018)

cornsnicker3 said:


> If the SlaythePE practice exam is royaling beating me up, this more indicative of my lack of preparedness or the difficulty of the practice exam?


Yes just probably more practice, I am going to take the TFS Exam this April as well. 

I looked into the Slay The PE TFS Sample Problems(The Free TFS Sample Problems Posted On their website) and I could answer them right away after reading the question(most by just using my calculator since most data are given) I am planning to buy the complete set in case I run out of problems prior to test date. I think the practice problems of SlayThePE is like a more detailed version of the NCEES practice test,  the difficulty is about the same with the NCEES Practice Test. 

I got lucky I got my hands on the 2001 NCEES Practice Test for $150. Its very hard to find.


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## cornsnicker3 (Mar 7, 2018)

Sheshtawy said:


> Probably lack of preparedness. But it's alright, you still have plenty of time to revisit the sections you're struggling with. The practice exam is very close in difficulty to the actual exam, except for a couple of heat exchanger problems which were just a bit too much.


Here is what is interesting. For just about all of the subjects, it is hit or miss if I "get" the problem. It doesn't seem like any one area is especially bad for me. It is like me being 50% with all of the subjects. I just received the Companion Problems to the MERM so I hope to seal up my understanding with those problems.


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## Sheshtawy (Mar 7, 2018)

cornsnicker3 said:


> Here is what is interesting. For just about all of the subjects, it is hit or miss if I "get" the problem. It doesn't seem like any one area is especially bad for me. It is like me being 50% with all of the subjects. I just received the Companion Problems to the MERM so I hope to seal up my understanding with those problems.


Well, that sounds like you need to solve more practice problems to complement your understanding of the topics. The MERM Companion should help immensely with that!


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## sambisu (Mar 7, 2018)

I just downloaded and printed out the Slay the PE practice exam and will be starting in on that this week. If I purchase the solutions, am I able to print them out or can they only be viewed digitally? I see they require a special PDF reader (which I won't be able to install on my work computer). So I was hoping I'd be able to print the whole thing and keep it at work with the rest of my study materials.


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## Slay the P.E. (Mar 7, 2018)

sambisu said:


> I just downloaded and printed out the Slay the PE practice exam and will be starting in on that this week. If I purchase the solutions, am I able to print them out or can they only be viewed digitally? I see they require a special PDF reader (which I won't be able to install on my work computer). So I was hoping I'd be able to print the whole thing and keep it at work with the rest of my study materials.


Yes. You can absolutely print them out.

Thanks!


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## cornsnicker3 (Mar 7, 2018)

Sheshtawy said:


> Probably lack of preparedness. But it's alright, you still have plenty of time to revisit the sections you're struggling with. The practice exam is very close in difficulty to the actual exam, except for a couple of heat exchanger problems which were just a bit too much.


When you say that the heat exchanger problems were too much, do you mean that for the actual exam or for the Slay the PE exam being too much?


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## Ramnares P.E. (Mar 7, 2018)

Created to clean up SlayThePE exam questions.  Also, please use this thread to discuss all practice exam difficulty issues going forward.

Thanks.


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## Sheshtawy (Mar 8, 2018)

cornsnicker3 said:


> When you say that the heat exchanger problems were too much, do you mean that for the actual exam or for the Slay the PE exam being too much?


Slay the PE questions were more difficult than the real exam for that particular topic


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## sambisu (Mar 9, 2018)

I'm only 14 questions in to the Slay the PE practice exam, but it seems noticeably more difficult that the NCEES practice exam. Definitely not a bad thing though. It's gotten me looking at and brushing up on some areas of the MERM which the NCEES exam didn't.


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## sambisu (Mar 9, 2018)

I'm hoping Slay the PE has licensing permissions for problems lifted from other texts...

View attachment 10904
View attachment 10903


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## Slay the P.E. (Mar 9, 2018)

sambisu said:


> I'm hoping Slay the PE has licensing permissions for problems lifted from other texts...


Sam,

You will find that maybe 10 or 12 of our test's problems are based on problems from Incropera for Heat Transfer, Cengel/Boles for Thermo, and Munson/Young/Okiishi for Fluids. Most have been changed more than this one you have pointed out, but you will indeed recognize the "core" of those problems.  The rest of our exam problems are originally ours.  

Our practice exam provides value even if you still have all those texts because the problems were carefully selected as being on topics relevant to the exam, helping you avoid working problems from them that would not benefit you. So our intention with those few problems was to present a carefully curated selection. If you don't have those texts, then the value from our exam is even greater since going and getting those texts would cost far more and you wouldn't have the benefit of knowing which problems to focus on.


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## mckenz007 (Mar 25, 2018)

Just completed a mock trial of this test, though I broke it up to 4/hrs over two days. 46/80.... nowhere near where I want to be &lt; 3 weeks out, but at least I’ve identified that I really struggle with all the power plant type questions. I have no memory of these types of problems back in school and certainly has nothing to do with my job now, but hopefully I still have time to figure them out between now and 4/13...


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## Suhaib Ahmed (Mar 26, 2018)

mckenz007 said:


> Just completed a mock trial of this test, though I broke it up to 4/hrs over two days. 46/80.... nowhere near where I want to be &lt; 3 weeks out, but at least I’ve identified that I really struggle with all the power plant type questions. I have no memory of these types of problems back in school and certainly has nothing to do with my job now, but hopefully I still have time to figure them out between now and 4/13...


Going through the Practice Exam right now and this is definitely harder and more detailed than the NCEES practice exam. Studying the material Slay the PE practice exam has is definitely beneficial but hoping the difficultly isn't similar to the actual exam! NCEES is a bit simpler so hoping it is more like that.


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## sambisu (Mar 26, 2018)

I felt like the first half of the Slay the PE exam beat me up a lot more than the second half. I felt much better after getting through the whole thing than I did about 1/4 of the way through. But I definitely found some weak areas I need to work on. Particularly compressible fluid dynamics and nozzle flow problems.


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## mckenz007 (Mar 26, 2018)

Now that I’ve actually had a chance to review some the solutions, I can see that many of the questions are actually quite simple if you can wade through all the superfluous information and focus on just what they are looking for. Everytime I saw a giant steam plant diagram my brain freaked out, but they really aren’t _that_ bad if you break it down... I’m looking forward at doing a second run of this test under that mindset...

Ohh compressible flow - I’m just reallllly hoping any of those questions will match the level of difficulty of the Ncees practice test


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## Slay the P.E. (Mar 26, 2018)

mckenz007 said:


> ...if you can wade through all the superfluous information and focus on just what they are looking for. Everytime I saw a giant steam plant diagram my brain freaked out, but they really aren’t _that_ bad if you break it down...


This is very much by design. You will see a few problems with a lot of unnecessary information to distract you and freak you out.  We wanted this to happen to you now and not for the first time during the actual test )


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## cornsnicker3 (Mar 27, 2018)

One thing that helped me recently with my effort on the NCEES practice exam was to ignore the data and focus on what was asked. I was always took a physics approach of start with what I needed to solve for and then fanning outward to find the missing constituents. One thing that really bugs me about Lindeburg's solutions for his MERM practice problem is that he works backwards. His methods are like throwing up all over the place and then coming together at the end. Not my favorite style.


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## sambisu (Mar 29, 2018)

cornsnicker3 said:


> One thing that helped me recently with my effort on the NCEES practice exam was to ignore the data and focus on what was asked. I was always took a physics approach of start with what I needed to solve for and then fanning outward to find the missing constituents. One thing that really bugs me about Lindeburg's solutions for his MERM practice problem is that he works backwards. His methods are like throwing up all over the place and then coming together at the end. Not my favorite style.


I agree 100%. My method is always to first try to identify the equation that involves the parameter I am looking for. Then I identify what I do and don't know in that equation and work backwards from there.


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## Vel2018 (Apr 1, 2018)

Anyone else saw that the key answer on problem 10 SlayPE is a typo? It is also like one of the merm companion problem but show different solution, specially the last step made in the slayPE solution. So which one is which to follow? Anybody have an idea?


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## MikeGlass1969 (Apr 1, 2018)

Vel2018 said:


> Anyone else saw that the key answer on problem 10 SlayPE is a typo? It is also like one of the merm companion problem but show different solution, specially the last step made in the slayPE solution. So which one is which to follow? Anybody have an idea?


Which Companion problem?

MERM Practice Problem 25-6?


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## Vel2018 (Apr 1, 2018)

MikeGlass1969 said:


> Which Companion problem?


Chapter 25 #6, this also velocity behind shockwave. Where if following SlayPE solution I can get the velocity as well after the shockwave. But Lindeburg did not do that to get the velocity behind the shockwave.


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## cfm03 (Apr 1, 2018)

Imo, both problems are correct. I think the text of problem 10 might need to be revised. Velocity (V1-V2) is actually induced velocity behind shock wave and V2 is the velocity behind shock wave. There are two different velocities. The problem 10 text needs to make the clear distinction between the two velocities...Let's wait for Slay's input to shed more light.


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## Slay the P.E. (Apr 1, 2018)

cfm03 said:


> Imo, both problems are correct. I think the text of problem 10 might need to be revised. Velocity (V1-V2) is actually induced velocity behind shock wave and V2 is the velocity behind shock wave. There are two different velocities. The problem 10 text needs to make the clear distinction between the two velocities...Let's wait for Slay's input to shed more light.


When our problem states that "_A normal shock wave travels ... through stagnant ...air._" and then we say "_the velocity (m/s) induced behind the shock wave_" it is all an indication that the frame of reference is stationary to the ground and not the shock wave. What velocity is induced on stagnant air right after the shock wave passes through? Our calculation shows that the air experiences an induced velocity in the same direction as the propagation of the shock wave. You have to momentarily use a frame of reference fixed to the wave because the equations are derived for such a frame of reference, but then you have to make the correction. This "correction" of course only applies to velocity. Thermodynamic properties (pressure, temperature, density) do not need to be changed. 

[COLOR= rgb(34, 34, 34)]In case of problem 25-6 in PPI's Practice Problems, they say "_the Mach number before a shockwave is 2_" -- here they have placed the frame of reference on the wave. The wave is stationary and the air in [/COLOR]front of it flows with a velocity such that M=2.


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## cfm03 (Apr 1, 2018)

Slay the P.E. said:


> When our problem states that "_A normal shock wave travels ... through stagnant ...air._" and then we say "_the velocity (m/s) induced behind the shock wave_" it is all an indication that the frame of reference is stationary to the ground and not the shock wave. What velocity is induced on stagnant air right after the shock wave passes through? Our calculation shows that the air experiences an induced velocity in the same direction as the propagation of the shock wave. You have to momentarily use a frame of reference fixed to the wave because the equations are derived for such a frame of reference, but then you have to make the correction. This "correction" of course only applies to velocity. Thermodynamic properties (pressure, temperature, density) do not need to be changed.
> In case of problem 25-6 in PPI's Practice Problems, they say "_the Mach number before a shockwave is 2_" -- here they have placed the frame of reference on the wave. The wave is stationary and the air in front of it flows with a velocity such that M=2.


Slay, you are correct. The problem's last sentence does say "induced velocity behind shock wave". The clarity has been there all along. Please disregard my earlier recommendation. 
My apologies...again I misseed important piece of information.


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## Vel2018 (Apr 1, 2018)

Slay the P.E. said:


> When our problem states that "_A normal shock wave travels ... through stagnant ...air._" and then we say "_the velocity (m/s) induced behind the shock wave_" it is all an indication that the frame of reference is stationary to the ground and not the shock wave. What velocity is induced on stagnant air right after the shock wave passes through? Our calculation shows that the air experiences an induced velocity in the same direction as the propagation of the shock wave. You have to momentarily use a frame of reference fixed to the wave because the equations are derived for such a frame of reference, but then you have to make the correction. This "correction" of course only applies to velocity. Thermodynamic properties (pressure, temperature, density) do not need to be changed.
> 
> In case of problem 25-6 in PPI's Practice Problems, they say "_the Mach number before a shockwave is 2_" -- here they have placed the frame of reference on the wave. The wave is stationary and the air in front of it flows with a velocity such that M=2.


"What velocity is induced on stagnant air right after the shock wave passes through?" - I don't know if I am looking at it right, but by your explanation it seems that the difference is where PPI problem the air is moving and shockwave is stagnant, and in your problem air is stagnant and wave is moving, so by just changing the frame reference makes the velocity behind the shock different? 

The thing that confuses me is both are still behind the shockwave, so no matter the air or the shockwave is moving, behind the shock is behind the shock?


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## Slay the P.E. (Apr 1, 2018)

Vel2018 said:


> "What velocity is induced on stagnant air right after the shock wave passes through?" - I don't know if I am looking at it right, but by your explanation it seems that the difference is where PPI problem the air is moving and shockwave is stagnant, and in your problem air is stagnant and wave is moving, so by just changing the frame reference makes the velocity behind the shock different?
> 
> The thing that confuses me is both are still behind the shockwave, so no matter the air or the shockwave is moving, behind the shock is behind the shock?


Yes. It’s the same velocity but its direction and magnitude change depending on the frame of reference.

Imagine a blast wave passing through a littered street. A bunch of debris and stuff will be “picked up” and fly in the direction of the wave, right behind it, but not as fast as the wave is traveling. This is what someone watching the thing go by will observe. They are “seeing” the induced velocity. But the imaginary dude riding on that wave will see the debris and junk actually traveling away from the rear side of the wave, but not as fast as he sees the air approaching the wave towards the front side.


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## Vel2018 (Apr 2, 2018)

Slay the P.E. said:


> Yes. It’s the same velocity but its direction and magnitude change depending on the frame of reference.
> 
> Imagine a blast wave passing through a littered street. A bunch of debris and stuff will be “picked up” and fly in the direction of the wave, right behind it, but not as fast as the wave is traveling. This is what someone watching the thing go by will observe. They are “seeing” the induced velocity. But the imaginary dude riding on that wave will see the debris and junk actually traveling away from the rear side of the wave, but not as fast as he sees the air approaching the wave towards the front side.


Exactly they are the same. The sample problem in the PPI air is moving, this is like the imaginary guy riding the shock wave, but the question is the same, there is a velocity induced behind the shock, the reference is the shock wave, same in you problem although the wave moves and air is stagnant; assuming both samples are travelling at same speed. Should we get a different magnitude of velocity behind the shock? 

The way I see it is only the observer changed its velocity but technically not the velocity behind the wave?


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## Slay the P.E. (Apr 2, 2018)

Vel2018 said:


> Should we get a different magnitude of velocity behind the shock?


Yes, we should. Our problem asks for velocity induced which is the velocity behind the wave measured from a stationary reference frame. Their problem asks for velocity behind the wave measured from a moving frame of reference. 



Vel2018 said:


> but the question is the same,


No it’s not. We ask for the induced velocity. They don’t.



Vel2018 said:


> The way I see it is only the observer changed its velocity but technically not the velocity behind the wave?


Correct.


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## Vel2018 (Apr 2, 2018)

Slay the P.E. said:


> Yes, we should. Our problem asks for velocity induced which is the velocity behind the wave measured from a stationary reference frame. Their problem asks for velocity behind the wave measured from a moving frame of reference.
> 
> No it’s not. We ask for the induced velocity. They don’t.
> 
> Correct.


PPI problem ask same, it is induced velocity behind shock, only difference there is the air was moving. There won't be any velocity induced if it weren't from the shock wave, no matter how you look at it air moving or wave moving shock wave is shock wave, and behind it was a velocity induced by the shock wave.

And with your question, although it did say that air is stagnant and wave is moving, since the *standard* of tables and graphs are made from the air is moving, I guess it just needed to add some clarity there what the problem is really looking for.

Because I don't think its right to assume that we have to measure the velocity while standing from a far looking at the wave unless specifically stated with "respect to observer, looking at the wave with X distance" etc again its because of the standard tables and graphs are not made this way.

It is like looking at the moon, and asking its size, size of it does not change no matter you go near or far, its size has already been measured its a fact. *(same with velocities behind shock)*

Unless you specifically ask with respect to your location what is its size, then there I can say its an inch. Its the same with this problem #10. If you ask whats the velocity induced by a 600m/s shock wave, it would be the same with air or wave moving, but if you ask to measure it with respect from a stationary observer then ok you are right.


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## Slay the P.E. (Apr 2, 2018)

The wording of both problems make it very clear which frame of reference each one is using. 

Why would you report a velocity behind the wave measured from the wave when it is your understanding from the problem statement that you are working with a reference frame on the ground?

For example: 

A man on a bus stop sees a car traveling east at 50 mph and a train next to the car also traveling east 20 mph faster than the car. What is the velocity of the train?

would you answer 0 mph because that is the velocity of the train with respect to an observer on the train?


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## Vel2018 (Apr 2, 2018)

Slay the P.E. said:


> The wording of both problems make it very clear which frame of reference each one is using.
> 
> Why would you report a velocity behind the wave measured from the wave when it is your understanding from the problem statement that you are working with a reference frame on the ground?
> 
> ...


would you answer 0 mph because that is the velocity of the train with respect to an observer on the train? ---&gt; Well of course not, the question is not the speed of the train but the speed that was left behind caused by the shock, which would be the same irrespective if the shock moves or the air moves. The only function of that velocity behind the shock is the actual velocity of the shock itself, it doesn't matter if you are on it or you are watching it from afar, the velocity behind the shock is the same. 

This is what it did on the problem as I understand it, the velocity behind the wave had a negative value(this is the velocity induced by the shock wave) then it subtracted it to the actual speed of the shock, what do you get is the speed of the "shock wave" relative to the velocity induced by it (not the velocity induced behind it). But this wasn't the question being asked.


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## Slay the P.E. (Apr 2, 2018)

Vel2018 said:


> ... it doesn't matter if you are on it or you are watching it from afar, the velocity behind the shock is the same.


This is not correct. The magnitude and direction of any velocity depends on the frame of reference; i.e. literally if you are on an object or are watching said object from afar. If you’re on the wave you “see” the air downstream going away from the wave. If you’re on the ground you see the air downstream of the wave going in the same direction of the wave. Both magnitude and direction are different depending on where the observer is. Do you agree?

Once you establish the frame of reference you use your calculation tools (in this case the tables) and then you report your velocities in the frame of reference being used in the problem. Right?


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