1. ## I made a math problem for my boyfriend...

My boyfriend asked me to make a math problem for him so I did... I don't know the answer

for sure, just wrote the question.
I was hoping someone could solve it on here, to let us know who was closer to the answer.
It might even be unsolvable... I'm not positive. :P

This is the question:

If a plane is landing and it has 1,858 metres before it has to stop/park the plane, and at the

beginning of landing it is going 80km/hr, how many km per 5 seconds does the plane have to

decrease speed?

This is my work:

The plane will park in 83.4 seconds:
80,000m/60min = 1,333.33m/min.
1,858m/1,333.33m = 1.39min
1.39min = 83.4 seconds

The plane is going 22.22m/second:
1,333.33m/60 seconds = 22.22m/1second.

The plane has to decrease its speed 16.68 times:
83.4/5 seconds = 16.68.

I don't really know where to go from here. :P

2. Originally Posted by fumirei
… how many km per 5 seconds does the plane have to decrease speed?
Can you rephrase this part? It's an odd way to ask about deceleration. Or, did you design the question itself to be a riddle?

"km per 5 seconds" is a rate (speed). It's the same as saying 0.2 km/sec (which is equivalent to 720 km/hr).

So, it seems like your question asks how many reductions of 720 km/hr are required to stop the plane. But, the landing speed is only 80 km/hr (must be a glider).

The plane will park in 83.4 seconds.
80,000m/60min = 1,333.33m/min.
1,858m/1,333.33m = 1.39min
1.39min = 83.4 seconds
83.4 seconds is roughly the amount of time it takes the plane to roll 1858 meters, if it does not slow down at all (or even stop)!

There may be round-off error in your result, as well. I get 83.61 seconds.

Time = Distance / Rate

= 1.858/80

= 0.023225 (hr)

To convert hours to seconds, multiply by 3600:

0.023225 · 3600 = 83.61 (sec)

Please re-think your question, and don't forget that slowing the plane increases the total time required to travel 1.858 km. The more the plane slows, the longer it takes.

3. Originally Posted by fumirei
My boyfriend asked me to make a math problem for him so I did... I don't know the answer...

It might even be unsolvable...
Math (and physics) questions are solvable, assuming enough information is provided. For instance, to stop a landing plane, one needs to know such things as:

. . . . .weight of the plane (including passengers, cargo, and fuel)

. . . . .braking power (not only the actual brakes, but also the thrust reversers, and when these are employed)

. . . . .flaps (degree, when extended, etc)

. . . . .winds (head-, tail-, or cross-, and speed; gusts and directions)

. . . . .condition of tarmac (dry, wet, icy; recently resurfaced or not; etc)

I'm sure there are other considerations. If any of the helpers here is, or has been, a pilot, you may receive other parameters. What information has been determined for this exercise?

Originally Posted by fumirei
If a plane is landing and it has 1,858 metres before it has to stop/park the plane, and at the beginning of landing it is going 80km/hr, how many km per 5 seconds does the plane have to decrease speed?
Do you mean that the plane needs to "decelerate to safe taxi speed before the end of the runway", or does your distance indeed include the taxiway, etc, all the way up to the gate? If the latter, how much runway does the plane actually have? Also, as mentioned, the specified speed does not sound like a passenger jet. Are we to assume a small single-engine prop plane, so we have no thrust reversers, and are relying entirely on brakes and flaps?

What types of mathematics and formulae are you expected to use? Calculus-based physics, or something else? Please be complete. Thank you!

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