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YAMT (Yet Another Math Thread)

B

bleeb

Lifer
A helicopter traveling at an average speed of 225 km/h left san jose 1 h after a train that had departed at 7:00 am. If the helicopter overtook the train in .8 h find the average speed of the train.
 
C'mon smart guys.. if this is 3rd grade stuff, the answer should be posted already.... but so far, looks like there is major homework avoidance going on here.
 
0.8 hr * 225 km/hr = 1.8 hr * x km/hr

100 = x km/hr

We know the time for which the helicopter has been travelling, the rate at which it is travelling, and the amount of time for which the train has been travelling (1 hr lead + 0.8 hr). We can create an expression for the distance each vehicle has travelled, and by equating the two expressions we capture the point at which their distance travelled is equalled (i.e. where the helicopter has overcome the train).

After that it's some multiplication and division, and you're set.
 
It's NOT 3rd grade math. This is more like 9th grade math.
<---- math teacher. (and physics teacher)
 
But, to solve it, figure out how far the helicopter travelled in that amount of time at that average speed.
Then, realize the train was travelling 1 hour longer....
If they left the same place, they've travelled the same total distance.
So, use the distance and the 1.8 hours to find the average speed.

Then, write next to your answer: "assuming both travelled on identical paths."
 
Originally posted by: DrPizza
But, to solve it, figure out how far the helicopter travelled in that amount of time at that average speed.
Then, realize the train was travelling 1 hour longer....
If they left the same place, they've travelled the same total distance.
So, use the distance and the 1.8 hours to find the average speed.

Then, write next to your answer: "assuming both travelled on identical paths."
Click to expand...

Also you must assume that there was no negative resistance... and we didn't account for acceleration factors, humidity, earth magnetic fields, wind resistance, jet stream and day light savings time.
 
For extra credit, point out that the "real world" problem does not deal with real world circumstances. Since you object to having to make an ungodly number of assumptions (ex - the helicopters speed was relative to the ground, rather than air speed, straight paths, etc) state that YOU are going to assume that they left in opposite directions.
Thus, .8(225) +1.8(x)=circumference of the earth. (for maximum x)

Ask you teacher when they built the bridge across the ocean.
 
OMG, I just realized... it's a trick question.
The train is barely moving at all! The helicopter flew in one direction for .4 hours, then realized they went the wrong way. Turned around, and caught up to the train .4 more hours later, 1 foot past the station.
 
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