## Goldman Sachs Interview Question for Financial Software Developers

Country: United States
Interview Type: Phone Interview

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13
of 13 vote

Here is the right answer, but could not think of when i was asked this question
Put plane on a ship which is in water and mark the hull immersed in water, then remove the plane from ship and start loading ship with known weights and the weight with which ship's hull comes to same marked position is the weight of plane.

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4
of 4 vote

Number of tyres * Amount of pressure in each tyre * surface are of the tyres

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3
of 5 vote

Airplane is a vehicle , so we can go the over the list of all materials used and their specifications and get the total weight. Not a very smart answer , but I think not a bad one too...

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0

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0
of 0 vote

As it is a well known fact that anything immersed in water displaces an equal amount of water as of its weight ...so putting the plane inside water and weighing the water displaced by it will give the plane's weight.

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1
of 1 vote

I was also asked same question by GS, but interview kept on asking what else other approach can you think of. But i couldn't give the answer he was looking for.
I searched on internet and found the solution, which was put plane on a ship which is in water and mark the hull immersed in water, then remove the plane from ship and start loading ship with known weights and the weight with which ship's hull comes to same marked position is the weight of plane.

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1
of 1 vote

this is just wrong. The water displacement is for calculating volume of water. If I submerge a galloon of milk with or without milk inside they would displace the same amount of water!!

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0
of 0 vote

Use a rope and try to just move the aeroplane while measuring the power consumed by the vehicle trying to move the plane...now from this you can calculate the force that was required to just move the plane. Now calculate the coefficient of friction of the tyre using a model. Now you know the force needed to move the plane and the coefficient of friction use this to calculate the wieght of the plane

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0
of 0 vote

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0
of 2 vote

Just pull the plane with a known force. say F. Calculate the velocity of the plane. Then neglecting force of friction.

F = 1/2(m)v^2

as initial PE being 0.

calculate m. weight will be m*9.794 i.e m*g (g being 9.794 in delhi). Best and the most practical way.

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0

Friction normally counts for minimum of 20% of its weight :)

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0

To calculate exact weight (not rounding off the co-efficient of friction)
Pull the plane with different forces F1 and F2 (F1>F2)
The equations would be as follows
F1=Work done by friction + 1/2(m)(v1)^2
F2=Work done by friction + 1/2(m)(v2)^2
Work done by friction will be constant in both cases as co-efficient of friction and normal force does not change

now take the diff
F1-F2=1/2(m)(v1)^2-1/2(m)(v2)^2

we know F1,F2,v1 and v2 and calculate m

Assumptions: Force F is applied along the centre of mass of plane so that it does not interfere with normal force.

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0

Calculating the weight based on friction is doubtful for me. I mean suppose if the plane is on wheels and we apply a force F the velocity will be higher compared to the same force applied when there are no wheels in plane. In case there are no wheels the friction will be more. These factors should be considered?

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0
of 0 vote

It can also be done by multiplying the air pressure in tires with the respective area of tires touching the ground surface.

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0
of 0 vote

Number of tyres * Amount of pressure in each tyre * surface are of the tyres

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0
of 0 vote

Bring something and lift the airoplane with it, The Force that airoplane starts to be lifted be some F. then just do m = F/g.

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0
of 0 vote

If we have access to the manufacturer's specs., the mass should be in there, but that's not weighing...
Standard weighing stations are used for weighing large vehicles like buses.
Use 3 positioned under the landing carriage and sum the measured weights.

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0
of 0 vote

Air pressure in the tires. Find it before installation. Also find volume before and after installation. Then find the air pressure after installation. The difference is due to airplane mass.

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0
of 0 vote

1. Component weight
2. Water displacement theory
3. Newton law of f=m/a -Apply a constant force and get an acceleration.. then get the weight which would be approx.
4. Tyre pressure thing
5. Get a prototype of the same specification, same set of components and determine its weight.. Once determined, scale up to the original specification ratio

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-1
of 1 vote

Move a plane with a known force then use accelerometer to calculate the accelerated velocity of plane then m=F/a.

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-1
of 1 vote

A pressure plate... this is a bad question

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-1
of 1 vote

Some weird ways that I can think of:

1) Attach the aeroplane on to a giant spring, and let it oscillate. Find period of oscillation and solve the equation for mass thereafter.

2) Throw the aeroplane from a certain height. Let it hit the ground on a pressure measuring device. Then get force and solve for mass using 'g'.

3) Use the aeroplane as a 'hammer' - yes, which is used in hammer throws. Tie it to a large enough 'rotating' device. Throw the aeroplane into the air at a certain velocity. Measure the distance from the point of throw to point of fall. Get the force from that and solve for mass thereafter.
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