Another puzzle !! - Page 2

N.geNuity

United States5112 Posts

November 01 2009 18:28 GMT

#21

yeah, which is why donnie doesn't run at a constant speed. If he ran only to point B, his speed is lower than if he gets hit exactly at point A. Running to point B gives him 12 km/hr (60/5). Running to point A gives him an average of 15 (where he can run 15 the entire time, or run 12 for one tick and 20 for the other tick. The average is 15 either way).

his "t" is not constant if he changes his speed. But his average works out to 15.

Average speed = |d| /time. He runs 2 ticks in the time it takes the train to go 8. His average speed is 1/4 the train. Thus it is 15.

If you run a 100m race, and run 99.9 metres in one second (99.9 m/s), then stopped and did the last 0.1m to finish at exactly 10 seconds, your average is 10 m/s.

When he averages 15, you can think of it this way:

5/8 * 12 + 3/8 * 20 = 15 km/h.

JeeJee

Canada5652 Posts

November 01 2009 18:42 GMT

#22

lol
i believe the problem here is that n.genuity thinks that the train is drawn relative to the 2d graph, when it's not. it's not 5 bars away from point b, you don't know how far away it is (although you can work out it must be 3 bars given the constant speed constraints)
if you think it is drawn to scale, wouldn't the train be about 4.25 bars away given that the front of the train will hit the person rather than the wheel?

Thats_The_Spirit

Netherlands138 Posts

November 02 2009 10:15 GMT

#23

I shouldn't have drawn the ticks all the way to the train, cause the distance from the train to donnie was supposed to be irrelevant.
Sorry for the confusion.

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