# Which of the train engines will reach first?

#### avi

Suppose that there are 2 identical train engines that moves on parallel railroads. Snow falls down in same way on both. On top of one of the trains there is a special equipment (weighs 0) that after every few seconds removes the snow from the roof of the train engine. Which of the trains will reach first and why?

#### oz93666

Will a snow laden train offer more wind resistance???

Will a snow laden train be heavier??? will a heavier train move faster or slower???

#### avi

Assume that snow lay vertically on the train in the same way. No friction and no wind. The snow influence only by its weight.

#### HallsofIvy

So the only difference is that the second train will be heavier than the first. How does that affect the speed?

#### avi

It has something connected to momentum and Newton 3rd rule. The first train the snow is accumulated all the time whereas the second every X seconds the snow is removed. I now that the first will reach faster. I don't know why?

#### Woody

These weird questions that invite us to apply theoretical ideas to awkwardly constructed impractical situations seem to abound in tutors text books.

It introduces "magic" snow clearing, but then expects a practical answer.
As Oz says, is it the mass that we need to consider, or is it the air resistance,
or is it the momentum lost to the magically removed snow, or...

The answer to that probably lies in the subject of the preceding lesson from the tutor.
If the tutor has been lecturing about mass, then assume it is the mass of the snow.
If the tutor has been lecturing about air resistance, then...

1 person

momentum

#### HallsofIvy

"Momentum"?

"Conservation of momentum" says that mass times velocity will remain constant. If the mass of one train is less than that of the other but they have the same momentum, what can you say about its velocity?

#### oz93666

there could be a clue in the fact that the snow "lies vertically" this has to be the forward face of the train ...

but then the second train melts and " removes the snow from the roof of the train engine"...

This is stupid , I think avi is making it up as he goes along ...

If not then he should give the full and complete question , this should have been done in post one.

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