SpaceX Interview Question: When a hot dog expands, in wh... | Glassdoor

Interview Question

Propulsion Structural Analyst Interview(Student Candidate) New York, NY

When a hot dog expands, in which direction does it split

  and why?
Tags:
analytics
Answer

Interview Answer

99 Answers

134

The stress in the circumferential/tangential direction is always larger than the stress in the axial direction, so it splits in long seams down its length rather than in hoops around its circumference. The equation for hoop stress is pr/t, whereas the equation for axial stress is pr/2t. It is a good exercise to derive these equations yourself.

Interview Candidate on Jul 29, 2015
15

To its weakest part

B on Mar 29, 2016
8

Splits lengthwise because the diameter is less than the length.

Tc on Mar 29, 2016
8

It splits along the long axis, the shear stress is greatest there. Materials always fail in shear, which is a combination of normal and tangential forces.

Hank Rausch on Mar 29, 2016

This post has been removed.
Please see our Community Guidelines or Terms of Service for more information.

47

It splits along the slits I put in it before I started to grill. Clearly you need someone that knows how to grill.

Dave on Mar 29, 2016
8

So for the most part answer one is correct. But it is not the stress its the strain that causes the failure. Plus most dogs have a slit which is a built in "defect" weak spot and it fails at the weakest point.

Eric Burke on Mar 29, 2016
29

It splits in the path of least resistance. It expands & cooks proficiently where resistance is greater, yet achieves desired results. Much like I will do as a member of your team. And as a comforting side note, although my confidence in my abilities is apparent and justified, my co-workers have never labeled me a hot dog.

Mike on Mar 29, 2016
6

It explodes on both ends, trust me , I have seen this happen. Otherwise, down the middle.

Vincent on Mar 29, 2016
6

Right down the middle like any good deep fried Texas weiner should.

Eric on Mar 29, 2016

This post has been removed.
Please see our Community Guidelines or Terms of Service for more information.

1

th

Anonymous on Mar 29, 2016
1

from inside out

Anonymous on Mar 29, 2016
1

It splits vertically. I only answer this way because it's what I've seen, although I don't know why.

Anonymous on Mar 29, 2016
1

It usually breaks lengthwise because the casing has some elasticity to it but there is more stretch in the length than the diameter because there is more casing in that direction, therefore it breaks lengthwise..

JK on Mar 29, 2016
0

Heat makes it expand in both directions. The weakest point is at the middle that splits alongside due to pressure produced by vaporization of water.

JEF on Mar 29, 2016
0

Both Ways

Dan on Mar 29, 2016
4

Oposite your mouth.

Georgi on Mar 29, 2016
1

If it's a quality dog made with authentic ingredients, it'll split along the seem. If it's a cheap dog made with synthetic ingredients, it'll break in half because it doesn't have the integrity of a genuine product.

Anonymous on Mar 29, 2016
0

It will split along the length because there is more of the "skin" to stretch than if it were to split the short way.

Lb on Mar 29, 2016
0

In both deriction

Anonymous on Mar 29, 2016
1

It depends on what type of casing the hotdog has. If it is man0made casing then they tend to split length wise. The man-made casings usually have a casing line down one side which seems to be the weak point in the product.

Mark on Mar 29, 2016
1

1, I have no idea.
2. When objects are heated, they expand due to molecules moving fast. The outer csing of a hotdog will split open if heated longer than necssary becoause of a seam in the casing.
3.I have no idea. I don't eat hotdogs.

Anonymous on Mar 29, 2016
0

lengthwise, expansion around smallest diameter of dog is greatest, and small tear forms and continues as expansion continues

scot swartz on Mar 29, 2016
0

They split at the weakest seam, just like my apostrophe in my last name on Unix servers.

Richard O'Brien on Mar 29, 2016
1

It splits apart, letting the heat escape from the core

Tyrone Gibson on Mar 29, 2016
6

That's an outstanding question, which I am extremely happy to answer for you, in detail!! But first, let me explain how a flux capacitor works, and more specifically how it applies to 'time travel'....

Punk Chicken on Mar 29, 2016
0

Does this question have anything to do with the position? If not, thanks for the interview. Don't call me, I'll call you. If yes, lengthwise.

Greybb on Mar 29, 2016
4

Depends in the breed.

PETA on Mar 29, 2016
0

It splits upward because of the gases that release upward through heat.

Jesse Jong on Mar 29, 2016
0

horses are for ride .....and above all question does not suggest they are attacking so no question for fighting

prabhat on Mar 29, 2016
0

The Hotdog splits lengthwise, but I don't know why.

It splits along the length on Mar 29, 2016
0

Most likely at one end horizontally

Anonymous on Mar 29, 2016
0

Lengthwise

G. Pendergrass on Mar 29, 2016
1

Why is it expanding? Is somebody cooking it or has it just been lying around getting rotten? Did somebody toss it outside of a spacecraft or are they filling it with air? Not enough info.

Al Luckow on Mar 29, 2016
0

The last time I over cooked a hot dog it split at the middle along the length of the dog

AnG on Mar 29, 2016
0

A frankfurter will split along the longitudinal axis because that's how it's always been done.

Actually. I know it has something to do with the skin/casing is stronger latitudinally, but I can't explain why.

Dale on Mar 29, 2016
3

#1 is correct (hoop stress vs axial stress) and the main reason for the lengthwise split, but you should also mention (for a manufactured casing) that the machine direction (as the casing was extruded) has better crosslinking than the cross direction (and thus can take more stress.)
This is the reason a plastic bag tears in a vertical line, not horizontally. (they are extruded as a tube and sealed, so the machine direction is vertical)
And as another answer pointed out, surface stress concentrations (such as the "grill" marks) will also cause the casing to fail.

plastic bag manufacturer (a long time ago) on Mar 29, 2016
0

Generally down the center

Anonymous on Mar 29, 2016
0

Down the middle lengthwise and later at the ends.

The casing is cut open to remove the cooked dog leaving a weak spot down the center. The ends are weak where the dog is "pinched" to size in the extruder.

Next...

Allie on Mar 29, 2016
0

Okay, forgot the part about steam expanding. Seriouly, it's a hot dog and a bs question.

Allie on Mar 29, 2016
0

diam expands / casing is weaker on diam

Anonymous on Mar 29, 2016
1

horizontally because of the pressure of the casing around the hotdog, and less pressure horizontally

Anonymous on Mar 29, 2016
0

It splits in a seamlike fashion across the middle line along the top, lengthwise in horizontal position, due to the fact that steam rises to the top.

Anonymous on Mar 29, 2016
0

I splits length wise because how the meat expands inside the skin.

Anonymous on Mar 29, 2016
0

vertical

Anonymous on Mar 29, 2016
1

depends on the manufacturer of the hot dog, its SKU, the price you paid for it, what day you bought it, from which store you bought it, how long you have had it, how quickly you have heated it, and other factors too many to list.

fara on Mar 29, 2016
0

Along the seAmsterdam of the dog.

Anonymous on Mar 29, 2016
0

It splits lengthwise, because the circumference is far less than the length, so there is less ability to stretch in that direction. The skin of the hot dog can more easily stretch lengthwise. Hence it splits perpendicular to the circumference.

Erle Spencer on Mar 29, 2016
0

Hot dogs split horizontally down the middle and occurs due to operator error as a result of cooking at too high of a temperature.

Anderson on Mar 29, 2016
0

In both directions if it gets really excited.

Abby Normal on Mar 29, 2016
0

The middle because there is room to stretch. The ends aren't.

Anonymous on Mar 29, 2016
0

Middle

Biff Widig on Mar 29, 2016
0

It splits lengthwise because - as its circumference expands - it gets thicker. The skin casing becomes tight as the water molecules heat up, and eventually splits from one end to the other. The pressure on the inside of the hotdog is evenly distributed from one end to the other. That is why the split occurs lengthwise, as opposed to across the width of the hotdog.

Alyssa on Mar 29, 2016
0

outward

Anonymous on Mar 29, 2016
0

lengthwise, because it plumps and is weaker on the long side than it is on circumference

joe on Mar 29, 2016
0

I eat Ball Park franks. They split first on the ends because that is their weakest point as the meat inside seeks to expand.

Anonymous on Mar 29, 2016
0

It splits lengthwise, which is the path of least resistance, similar to a fault line in the earths crust.

Michelle on Mar 30, 2016
0

In my experience I have never seen it split any other way than down the middle. Why? No idea and I don't care.

Lori on Mar 30, 2016
0

when a weiner gets hot and expands it spits in the direction of the bun

Anonymous on Mar 30, 2016
0

Along the seam.

Alejandro on Mar 30, 2016
1

What is causing the hot dog to expand? Heat? Decrease in atmospheric pressure? Injection of foreign material? More information is required to adequately answer the question.

Double-Oh Savant on Mar 30, 2016
0

I'd say it splits lengthwise because that's what I've observed in microwaved hot dogs. I'm guessing that's basically with the grain. In other words, a hot dog is weaker that way.

Jill W. on Mar 30, 2016
0

axially

Anonymous on Mar 30, 2016
0

It splits where it is the hottest and also where the casing is the weakest. Why do you ask?

Anonymous on Mar 30, 2016
0

Thinking the hotdog is me, expand outward. I would like to expand all over the company. I would want to know the ups and down, also inputs and outputs of the company.

LoSonji on Mar 31, 2016
0

It expands in width not length.

John on Mar 31, 2016
1

At top heat rises

Dana on Apr 1, 2016
4

Hunh. A badly phrased question. From an Engineering company. Who would have thunk ? As far as hot dogs go, it varies, by brand and chance; My initial flash was that a hot dog splits lengthwise because the two endpoints are weak where the casing is sealed; I recall an image of a hot dog split along the long axis starting from one of the endpoints (Imagine a tea kettle). But this is obviously much more complex. Reading the various previous answers has opened my vision to such an explosion of factors : (a) Direction of the cylinder relative to the heat -- heat rises, steam pressure is upward? -- wow; (b) Lengthwise seam exists in some brands, who knew? -- (c) the casing is stronger depending on direction of extrusion of casing material at manufacture, somewhat like some woven fabrics, okay, that's news -- Hunh. So really we'd have to experiment with the subject hot dog(s) under relevant conditions. There isn't any other reliable method. There are too many factors that could go into the strengths and weaknesses of a hot dog design. Nice question I guess, or dumb question maybe, depending on what the question was designed to elicit. If SpaceX is founding its designs on hot dog dynamics though, that's a disappointment.

TheZosLady on Apr 3, 2016
0

It splits along the length of the dog. It expands in all directions.

Allen Paul Smith on Apr 4, 2016
0

Why are you eating hot dogs? Get some proper vittles.

Jeremy Hetrick on Apr 4, 2016
0

It splits outwards if cut down the middle.

Anonymous on Apr 6, 2016
1

It depends WHY it expands and HOW you define expansion.

Why 'how expansion is defined' matters: [Most] People are answering based on heating/cooking which would increase the volume of the entire hot dog which = expansion. If expansion, however, can include individual cross-sectional expansion rather than 'single unit' expansion, then as you bite into a [presumably cooked] hot dog, the internal structural change within the hot dog from the pressure of your teeth will cause cylindrical cross sections near the bite point to expand. It will split [presumably] horizontally with your teeth. Even if you assume the hot dog would have already split during the heating process, it would expand in this way again when you bite and would split again when you bit it.

Also, how do you define 'split'? Won't go there now....

Why 'why it expands' matters: Based on the above, the hot dog can be cooked or uncooked, so to expand it in order to split it, you can cook it, bite it, or smash it with a hammer and all of those will result in different 'directions of split' and also, maybe even multiple splits.

So my concise answer: It depends how it expands and how you define expansion, and even how you define split (split the surface vs split into separate pieces). To be [arguably] persnickety, when a hot dog expands it will only split once a critical point is hit, so it could also expand and NOT split.

Leo Emerson on Apr 8, 2016
0

Out

Mike on Apr 8, 2016
0

as i haw seen they can do when boiled and skin pop.

on the length on Apr 16, 2016
0

The real answer is why would you want to work for someone that ask such stupid questions

Dumbfounded on May 2, 2016
0

put it in a microwave... it doesn't split... it explodes.

Robert on May 2, 2016
0

Assuming the insides of the hotdog are more-or-less fluid, then pressure will be exerted equally normal to the casing at every point on the surface. However, the force which pulls the casing apart is related to the gradient of the normal vector and not just the normal itself. As the curvature is much sharper axially, the gradient will be higher for it to split lengthwise. This will cause a seam that grows quickly, resulting in long, length-wise splits.

However, we should also take into account any anisotropic structures in the casing itself. If the casing is made out of a bunch of long strips, it will split lengthwise even easier. If it is made out of a bunch of stacked rings, it will have hard time doing this and it probably wont split length-wise quite as easily. This is a question of intestinal physiology, and I suppose it depends on how the muscles work.

Anonymous on May 2, 2016
0

It splits lengthwise because each hot dog link is made by twisting the casing at the ends during the manufacturing process. This makes the ends more rigid and structurally sound than the rest of the casing.

Anonymous on May 13, 2016
0

It splits lengthwise at top - it is the casing that splits as someone else mentioned, but I think that what is responsible for the split are the juices that begin to boil inside the hotdog, and which will naturally rise to the top creating the pressure to split it. Once the pressure is released, it is done expanding.

Carrie Sampson on Sep 22, 2016
0

The Educated Answer: Most people prepare a hotdog by pricking it, or slicing it lengthwise to reduce the circumferential and axial expansion due to the gases released from the heat source and the ingredients of the hot dog.. Most heat sources are due to: grilling, boiling, or microwaving. The expansion is also affected by the contents of the hot dog: chicken, turkey, beef or combination. I have noticed significantly less expansion of gaseous expansion circumferential and axial in beef kosher products with less fillers , sodium and preservatives. It is most likely to see a lengthwise gaseous expansion in most hot dogs depending on the cooking temperature, method,preparation and ingredients of the hot dog.

Hot Dog Preparation and Expantion on Sep 22, 2016
0

Lengthwise, because it has to expand in the direction that gives it the most opportunity for growth.

Anonymous on Sep 23, 2016
0

This question essentially asks you whether or not you understand stresses in pressure vessels and the most common failure mode involved. The failure will be propagating lengthwise (unless "meat product" is not homogeneous) when far away from ends.

Anonymous on Sep 26, 2016
0

It would split lengthwise because the ends are scrunched up and thicker than the middle part.

Anonymous on Sep 30, 2016
0

From the middle outward & lengthwise, following the seams of the hotdog being that it is the weakest part & mostly in the middle because the ends are compressed.

Martiana on Oct 4, 2016
1

I'm a vegetarian so I'm not interested in hot dogs!

Farid on Oct 12, 2016
0

Besides to its entirety of expansion and direction, it always depends when it's cooked or uncooked,also it depends on its longevity of cooking and when this was processed as well.

An expanded hotdog depends when it's cooked or uncooked not only that it also depends if it's fresh on Dec 2, 2016
2

How about inviting me to the company barbecue? We can test several different brands and hypothesize in real time.

Anonymous on Jan 6, 2017
0

The hotdog splits in a vertical pattern first and then horizontally if too much heat or pressure is applied. The outer layer splits first which is the vertical aspect of the reaction. Then the split extends horizontally on the hot dog resulting in the cracked skin and loss of juices.

Aaron Shaw on Jan 19, 2017
0

It splits along the middle, because that's easiest for it, physically.

Courtney on Feb 2, 2017
0

Hoop stress > Longitudinal stress

Anonymous on Feb 8, 2017
0

Similar to 99% of question asked during interview. They are not interested in the answer unless specified, they just want to see how is your reaction and response to any difficult questions.
So re-phrase the question as how do you response to stress under extreme situation. Diversion & delay in response are one of the best technique as not to commit anything under duress situation that might cost company suffer a huge lost.

Anonymous on Feb 20, 2017
0

vertical

Mimi on Mar 9, 2017
0

I agree with #1 that [the strain induced by] hoop stress vs. axial stress is the main cause of the longitudinal hot dog failure. As stated by others above, possible additional contributions include localized stress concentrations, weak seams from the hot dog production process, pre-cut slits, and (as stated by "plastic bag manufacturer") machine-direction vs. non-machine-direction effects in the hot dog casing. Given the assumed context of thermal expansion in the process of grilling a hot dog, this is the correct answer.

When asked this question in an interview, the actual correct response is to first clarify the assumptions behind the question by asking a critical follow-up question or two:

By what means is the hot dog being induced to expand? The default assumption for most people would be thermal expansion due to heating on a grill, but the situation is quite different if the hot dog is expanding due to the Poisson effect from someone squeezing it.

What is the surrounding environment relative to the hot dog? The default assumption is that the hot dog is being heated on a grill, but the situation is quite different if the hot dog is expanding in a pressure chamber under controlled conditions.

Geotechnical Engineer on Apr 7, 2017
1

It expands sideways and splits from the center, long ways.
This may be the most simple answer to the question but the actual answer will depend on the relevance of this question to the job applied for.

Samar on May 23, 2017
0

Ends first, lengthwise next and if cooked long enough the possibility across the center of the hot dog.

As the meat expands due to cooking, tension on the casing will cause the cut ends to split first due to them being the weakest points. This allows the meat inside to easily expand out the ends reducing tension across the width of the casing . However tension lengthwise continues until the casing splits. Cooked long enough the hot dog can split across the hot dog as well.

The method in which the hot dog is cooked also plays a factor. Microwave or open flame will cause more tension on the casing due to moisture leaving the casing. Boiling will allow the casing to be more pliable allowing the casing to expand more before a split occurs.

Brian Rininger on Jun 21, 2017
0

equally in all directions

Tracey Rogers on Nov 26, 2017
0

upwards, the portion of the hot dog that is opposite of the side that is laying on the heat source, because pressure builds and that is the side of least resistance.

sue rasmussen on Mar 11, 2018
0

First it depends on how it’s presented, horizontally or vertically. If it’s presented horizontally then you could answer the same way and Visa versa. You could simply answer “longways” too. The “and why” part of the question could be answered technically if you know your physics, or simply state, “Because you can’t teach an old dog new tricks...” to hopefully put a smile on their face.

Cassie on Jul 26, 2018

Add Answers or Comments

To comment on this, Sign In or Sign Up.