Why Do Tech Interviews Ask Physics Questions?

Apparently, these are questions that have been asked by Microsoft interviewers:

1) You are on a small boat at the sea with a trunk as luggage. If you throw it out of the boat to the water, Does boat raise?

2) How would you weight a Jumbo plane without using a scale? (I know one very good answer replied by an applicant engineer)

Were they interviewing Archimedes for a job? I'd hire him!

Njorl

weight = (MassOfPlane(in kg) x MassOfEarth(in kg) x G (the gravitational constant )) all divided by the square of the distance in meters between the centre of mass of the Earth and the centre of mass of the plane. You may want to check this.

Another way of doing it is when the plane is on the ground, place some type of heavy duty airbags under the landing gear. Use a hydraulic ram to fill the bags by placing weight on the ram. The total amount of weight placed on the ram, when the plane begins to rise, is the approximate weight of the plane. In this answer, I would also explain that the bags weighed a certain amount and then multiply the sum of all the bags by the lift ratio of the ram.

As far as the boat goes: The sea would still displace if you threw a rock into it that didn't come from the bottom. The boat would raise due to the displacement of the objects (luggage) thrown in. This is definitely an order of magnitude operations answer. The answer could really go either way. The volume of the sea is basically infinite so throwing luggage into it would not equate to much displacment. Drop an asteroid the size of Texas into the ocean and see if the boat raises up.

I guess I'm just not cut out for microsoft if they ask these sort of silly questions. How about asking what my hobbies are?

M2k

Originally posted by Tachyon son

2) How would you weight a Jumbo plane without using a scale? (I know one very good answer replied by an applicant engineer)

Consult the cut sheets

Originally posted by Tachyon son

2) How would you weight a Jumbo plane without using a scale? (I know one very good answer replied by an applicant engineer)

I guess I'm glad that I don't work at Microsoft since this second question is without meaning. To measure means to actually take a measurement. The question does not ask "How would you determine the weight given the mass" which is entirely different. A "scale" is defined as that which is used to measure weight and hence the question is meaningless.

If I were interviewing the person who created that question then he'd have failed that portion of the test.

Originally posted by Tachyon son
How would you weight a Jumbo plane without using a scale?

I'd ask for the air pressure in the tires and measure the deformation as it is parked.

Originally posted by krab
I'd ask for the air pressure in the tires and measure the deformation as it is parked.

In which case the tires are acting as scales. There is little difference since a spring scales uses Hookes law to measure force as would using the deformation of a rubber tire.

It is only forbidden to use a "regular" scale (i.e a balance). Therefore the method of krab it is allowed, but you need to precise what kind of calculation would you make.

2) How would you weight a Jumbo plane without using a scale? (I know one very good answer replied by an applicant engineer)

Can you give us the AE's answer? Or is that classified?

M2k

Originally posted by Tachyon son
Apparently, these are questions that have been asked by Microsoft interviewers:

1) You are on a small boat at the sea with a trunk as luggage. If you throw it out of the boat to the water, Does boat raise?

2) How would you weight a Jumbo plane without using a scale? (I know one very good answer replied by an applicant engineer)

For the answer of the 1st question:

Of course the boat raise :)

2nd:

I think there is any relation with the velocity of the plane and the time when it take of, right?

The best interview question I have seen is "How would you move Mt. Fuji?"

My answer, I would just wait, it is always moving anyway.

Regarding Question 1:

As long as the luggage is heavier than what it replaces it in the boat, the boat rises in the water.

If the luggage floats, the water level stays the same. If the luggage sinks, so does the water level.

So, if the luggage floats, the boat will rise.

If the luggage sinks, then the water level will drop, but the boat will rise in the water. How much the boat rises depends on the geometry of the boat.

Whether the

Regarding Question 2:

Calculate the total thrust the engines supply, and then measure the acceleration, or use a similar approach with a tow car.

Measure the pressure above and below the wings and calculate the net force.

Measure the change in the suspension springs while the plane is being fueled.

Create an exact scale model, and extrapolate, or use the blueprints.

Use large pieces of graph paper, a pencil or sharpie type marker and a tire gauge calibrated in pounds per inch (ppi). Place a sheet of graph paper beneath the tires of the aircraft and tow the aircraft onto the papers. Carefully outline the print of each tire on the graph paper. Measure the air pressure in each tire when it is outlined and make a note of the pressure. Remove the graph paper and count the total number of inch squares in the outline of the print. Take the product of the pressure measurement you made of each tire and the total inches in the outline. Add the totals for each sheet and that is how much it weighs. I think this is what the krabster was alluding to. Nice job.

M2k

The best interview question I have seen is "How would you move Mt. Fuji?"

Are you serious?

Interviews suck

Originally posted by MrCaN
The best interview question I have seen is "How would you move Mt. Fuji?"

My answer, I would just wait, it is always moving anyway.

Aham... My answer is more classical, you have to move your-self and tell, as every thing is relative...so if you are the frame of ref. the Mt.Fuji is moving! Right?

Originally posted by NateTG
Regarding Question 1:

As long as the luggage is heavier than what it replaces it in the boat, the boat rises in the water.

If the luggage floats, the water level stays the same. If the luggage sinks, so does the water level.

So, if the luggage floats, the boat will rise.

If the luggage sinks, then the water level will drop, but the boat will rise in the water. How much the boat rises depends on the geometry of the boat.

Whether the

I don't follow, so I disagree :p
If the luggage floats alone, that does not have to mean that it's presence IN the boat will not affect the boat's level.

Floating or not is based on the water displaced compared to the weight of the object, but you already know that.

The fact that the luggage is not displacing water at that point in time (directly) would mean that this is not part of this problem. The additional weight from the luggage, if any , will lower the boat in the water, even if it is only a very slight bit.

If your idea were true, then I could put an infinite amount of luggage in the boat, because none of them weight it down.

Let's continue, may more :D DON'T CHEAT *****ES!


3. You have 8 balls. One of them is defective and weighs less than others. You have a balance to measure balls against each other. In 2 weighings how do you find the defective one?

4. Why is a manhole cover round?

5. How many cars are there in the USA?

6. You've got someone working for you for seven days and a gold bar to pay them. The gold bar is segmented into seven connected pieces. You must give them a piece of gold at the end of every day. If you are only allowed to make two breaks in the gold bar, how do you pay your worker?

7. One train leaves Los Angeles at 15mph heading for New York. Another train leaves from New York at 20mph heading for Los Angeles on the same track. If a bird, flying at 25mph, leaves from Los Angeles at the same time as the train and flies back and forth between the two trains until they collide, how far will the bird have traveled?

8. You have two jars, 50 red marbles and 50 blue marbles. A jar will be picked at random, and then a marble will be picked from the jar. Placing all of the marbles in the jars, how can you maximize the chances of a red marble being picked? What are the exact odds of getting a red marble using your scheme?

9. Imagine you are standing in front of a mirror, facing it. Raise your left hand. Raise your right hand. Look at your reflection. When you raise your left hand your reflection raises what appears to be his right hand. But when you tilt your head up, your reflection does too, and does not appear to tilt his/her head down. Why is it that the mirror appears to reverse left and right, but not up and down?

10. You have 5 jars of pills. Each pill weighs 10 gram, except for contaminated pills contained in one jar, where each pill weighs 9 gm. Given a scale, how could you tell which jar had the contaminated pills in just one measurement?

11. If you had an infinite supply of water and a 5 quart and 3 quart pail, how would you measure exactly 4 quarts?

12. You have a bucket of jelly beans. Some are red, some are blue, and some green. With your eyes closed, pick out 2 of a like color. How many do you have to grab to be sure you have 2 of the same?

13. Which way should the key turn in a car door to unlock it?

14. If you could remove any of the 50 states, which state would it be and why?

15. There are 3 baskets. one of them have apples, one has oranges only and the other has mixture of apples and oranges. The labels on their baskets always lie. (i.e. if the label says oranges, you are sure that it doesn't have oranges only,it could be a mixture) The task is to pick one basket and pick only one fruit from it and then correctly label all the three baskets.

Hmmmm...

Originally posted by mighty2000
Can you give us the AE's answer? Or is that classified?

M2k

Take the airplane into a big ship. Mark flotation line before and after putting the plane. Remove the Jumbo and start adding sandbags (of 50kg for example) until leveling with the previously marked flotation line. Now you know the weight.

3. It's easy. Why not ask about 9 balls instead? Or how about 12 balls, with one lighter or heavier than the others and 4 weighings. Heck, for bonus points how many weighings would it take for 2004 balls with either one lighter or heavier?

4. There are many good answers to this question. The official answer is that:

Manhole covers are round so that they don't fall into the hole that they're covering.

But there are other shapes that have that property. There are some other good answers:

Manhole covers are round because manholes are round.

Manhole covers are round because the circle maximizes the area for the diameter. This means, among other things that the manhole cover is as thin/cheap as it can be if material is expensive.

Manhole covers are round because that is the 'de facto' standard.

5. Approximately 300 million

6. Break the bar into 1,2, and 4 segment pieces.

7. Assuming that the distance between New York and LA is 3500 miles, the bird will go 2500 miles.

8. The optimum is to put a red marble into one jar by itself, and the rest of the marbles in the other jar.

The odds are : [tex]\frac{1}{2}+\frac{49}{198}=\frac{148}{198}=\frac{74}{99}[/tex]

9. Because up and down are not self-relative. The mirror's 'left' had is still on your right side.

10. 0 from the first, 1 from the second, 2 from the third, 3 from the fourth, and 4 from the 5th.
If the measurment is w then 150-w+1 gives the number of the jar with the bad pills.

11.
Fill the 3 gallon bucket, pour it into the 5 gallon one
Fill the 3 gallon bucket again, pour into the 5 gallon one until the 5 gallon bucket is full.
Empty the 5 gallon bucket.
Pour the remaining gallon into the 5 gallon bucket
Fill the 3 gallon bucket.
Pour the 3 gallon bucket into the 5 gallon bucket.

12.
There are 3 colors, so I must pick 4 jellybeans.

13. There are lots of answers for this one as well:
Neither way, inserting the key should be sufficient.
Clockwise because that is the natural motion for right handed people.
Anticlockwise because that is the natural motion for unlocking the door with the left hand which puts the driver in the correct position for getting into the car.
Clockwise because that is the 'de-facto' standard
...

14.The state of denial
The state of Washington so these silly questions can come from somewhere else than Microsoft

15. Pick a fruit from the basket that's labled apples and oranges. Clearly that basked cannot be mixed, so you know that it must be the fruit that you picked.
The basked that has the lable matching the fruit that you picked has the other fruit, and the last basket holds the mixed fruit.

Originally posted by MrCaN
The best interview question I have seen is "How would you move Mt. Fuji?"

My answer, I would just wait, it is always moving anyway.

My answer-

I don't need to move Mt. Fuji. If my boss thinks I do, I will check with his boss. If his boss thinks I do, I will sell my stock options and look for a new company, because this one is about to go bankrupt.

Njorl

should some moderator remove this thread right about now? This has nothing to do with Physics. If I am not mistaken, Microsoft is a software company. The lab computers I work with actually runs Solaris.

Originally posted by mathfeel
should some moderator remove this thread right about now? This has nothing to do with Physics. If I am not mistaken, Microsoft is a software company. The lab computers I work with actually runs Solaris.

Sadly, I completely disagree with you. Actually, I started this topic asking PHYSICS QUESTIONS made by a company. IMHO it doesn´t matter if it is Microsoft or anyone else.

P.S: Would you feel more confortable if these PHYSICS QUESTIONS were from Sun Microsystems interviews?

Originally posted by Tachyon son
Sadly, I completely disagree with you. Actually, I started this topic asking PHYSICS QUESTIONS made by a company. IMHO it doesn´t matter if it is Microsoft or anyone else.

P.S: Would you feel more confortable if these PHYSICS QUESTIONS were from Sun Microsystems interviews?

Agreed. The first two questions were essentially about Archemides principle. Ask anyone what category to put Archemedes in and they should say general physics.

Njorl