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Challenge Questions

Stop in and exercise your brain. Talk about this month's Challenge from Specs & Techs or similar puzzles.

So do you have a Challenge Question that could stump the community? Then submit the question with the "correct" answer and we'll post it. If it's really good, we may even roll it up to Specs & Techs. You'll be famous!

Answers to Challenge Questions appear by the last Tuesday of the month.

Autumnal Glow: Newsletter Challenge (December 2014)

Posted December 01, 2014 12:00 AM
Pathfinder Tags: challenge question

This month's Challenge Question: Specs & Techs from IHS Engineering360:

It is a new moon and Lee is taking a predawn stroll on a beach on the east side of Nantucket admiring the stars. As he looks out over the Atlantic Ocean, he notices what seems to be the soft glow of light pollution from a city off in the distance. What is Lee seeing?

The answer to this challenge will be posted later this month, right here on CR4.

62 comments; last comment on 12/18/2014
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Icy Imbalance: Newsletter Challenge (November 2014)

Posted November 01, 2014 12:00 AM
Pathfinder Tags: challenge questions

This month's Challenge Question: Specs & Techs from IHS Engineering360:

The two poles of the Earth contain ice. Why does Antarctica have much more ice (about ten times more) than the Arctic?

And the answer is:

Ice in the arctic circle is over the ocean, while Antarctica is a solid landmass. Water has a high heat capacity, so it takes a long time to absorb heat, but also a long time to lose heat. During summer the Arctic water stores heat and in winter it releases it. On the other hand, land does not have a high heat capacity so it releases heat very fast, keeping the land to a lower temperature all year round.

20 comments; last comment on 11/26/2014
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The Merlin Rocket Engine: Newsletter Challenge (October 2014)

Posted October 01, 2014 12:00 AM
Pathfinder Tags: challenge question

This month's Challenge Question: Specs & Techs from IHS Engineering360:

The SpaceX Falcon 9 v1.1 uses nine Merlin 1D rocket engines in its first stage. The thrust of a Merlin 1D engine in a vacuum is 720 kN, about 10% more than its 650 kN thrust at sea level. Why does the thrust of the Merlin 1D increase with increasing altitude?

And the answer is:

The thrust of a rocket engine is equal to:

The first term is the mass flow rate of the exhaust gas in kg/s times the exhaust gas velocity. The second term is the product of the cross-sectional area of the nozzle exhaust exit and the difference between the exhaust gas pressure at nozzle exit and the external ambient pressure.

Essentially, sea level atmospheric pressure distorts the exhaust gas flow, lowering its cross sectional area, and making the rocket engine less efficient, thus lowering thrust.

46 comments; last comment on 10/28/2014
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Balloon Ride: Newsletter Challenge (September 2014)

Posted September 01, 2014 9:00 AM
Pathfinder Tags: challenge question

This month's Challenge Question: Specs & Techs from GlobalSpec:

You are inside a car with the windows closed, and you are holding a helium balloon by a string. You are cruising at 30 mph. Now you make a right turn. What happens to the balloon? Does it move to the left? Or to the right? Or does it stay in the same position? Find the right answer and explain the reason.

And the answer is:

The air inside the car tends to continue in the same straight-line direction (Newton's laws), so when turning the pressure on the outside radius of the turn will be a bit higher. Therefore the balloon will be pushed to the right (to the inside radius of the turn).

40 comments; last comment on 09/23/2014
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The Sprinkler Mystery: Newsletter Challenge (August 2014)

Posted August 01, 2014 12:00 AM
Pathfinder Tags: challenge question

This month's Challenge Question: Specs & Techs from GlobalSpec:

An old home's new sprinklers are scheduled to start up at 9 PM but do not. A tech manually turns on the sprinklers from the controller located in the basement boiler room. He hears from upstairs that they are working fine so he closes up the controller, goes upstairs and sees that the sprinklers have stopped working again. What's going on?

And the answer is:

Based on a true story from someone here at IHS, the Sprinkler Mystery gave us all a good laugh. It turns out the answer to the mystery was that the sprinkler controller was plugged into a switched outlet. When the sprinkler system tech went into the basement, he turned on the light, which also turned on the outlet for the controller. Thus the sprinkler started working. When the tech left the basement, he turned out the light, which turned off the outlet for the controller. The sprinkler stopped working. The solution? A little rewiring of the old house! Glad to report the sprinkler system now works great!

144 comments; last comment on 09/04/2014
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Space Trail: Newsletter Challenge (July 2014)

Posted June 30, 2014 12:00 AM
Pathfinder Tags: challenge question

This month's Challenge Question: Specs & Techs from GlobalSpec:

The path that a spacecraft follows when traveling to the moon is a distorted figure eight, instead of an ellipse surrounding the earth and the moon. Why is this?

And the answer is:

The reason is energy-saving. The figure eight path allows the spacecraft to remain almost equidistant from the centers of the earth and the moon. At this path the gravitational pull of the earth and of the moon attract the ship in opposite directions, so the net force exerted on the craft is minimized, and it is certainly smaller than the force exerted on an elliptical path.

21 comments; last comment on 08/10/2014
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