Can a fly really stop a train?

Question

A fly is travelling at 5 miles per hour head-on towards a train travelling at 100mph. As the train hits the fly it changes direction (as well as getting squished) and so starts travelling at -100mph. Which mean it has to pass through 0mph as it touches the train. If the fly is travelling at 0mph at the instant it touches the train, the puzzle goes that the train must also be travelling at 0mph. Is this right? I only got O'level Physics!

Answer 1

No, the train keeps going at 100mph relative to the ground for the whole time. The fly starts off travelling at 5mp relative to the ground and then later 100mph relative to the ground (in the other direction). However ... what is important is the RELATIVE velocity of the fly and the train. Initially it is 105mph, but after impact the relative velocity of the fly and the train drops to 0mph (i.e. they are moving together).

Answer 2

The fly traveled at 0mph only for a split sec and then it was travelling at 100mph again. The train never changed speeds as it never stopped, only the fly did.

Answer 3

This is applied Maths/Physics being used in a Purely Theoretical way.

We all know what REALLY happens; but the Boffins like to flex their Thinking Muscles!!!

Answer 4

A cow herd won't stop a train in any country, much less the flies around the cows.  I was due to take a freight from Kansas City to Des Moines and had a CSX loco with brown stuff all over the nose.  It was dried cow guts from where the cows had got on the tracks and didn't move in time.  It was nasty to say the least and it was summer too.

Answer 5

A fly can't stop a train...but a train can sure stop a fly.

Answer 6

Not one fly but a loads on the windscreen. its possible if theres thousands on the windscreen, travelling at 100mph, and the windscreen wipers maybe not be affective enough, If the wipers dont work, the driver had to fail the train or loco.

Answer 7

Only if it hits the driver in the eye  !!

Answer 8

The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. Negative work of the same magnitude would be required to return the body to a state of rest from that velocity.

If you look closely at the front of the train, you'll see that the fly NEVER did stop. The energy of the fly was distributed in an outward pattern at high velocity, and thusly only imparted it's energy in a different direction.

Answer 9

um... did u forget to take ur medicine in the moring.

Answer 10

Cad remembers this question from "HOW"(kiddies program 1977) the answer is still no.....

Answer 11

The only way a fly could stop a train is if it somehow became trapped in the emergency brake system, thus short-circuiting it and triggering the brake.

Most of the other answers are correct, i.e. the fly's mass is so tiny compared to the train that its impact on the train's velocity would be non-existent.

Answer 12

Yes - it's a very good question and it quite a complex one. The answer is no for a number or reasons.

1. The fly kind of reaches reached 0mph, but not all all of it does at the same time: if you think of a very big fly, then you will see that the first part of the fly's body to impact on the train will react differently to the latter part of the fly's body. The latter part will be slowed down by the first part, and crushed into the first part. The latter part can technically come to 0mph as it can do this while the first part of the body is now in reverse and moving at the same speed of the train.

2. Now back to the first part of the body. The train simply doesn't stop - it can't do - so what happens to the energy of the fly? Well, that is in part the splatter. The fly continues at a speed, or should I say the parts of it continue at a speed, but sideways, so the energy of the fly is deflected.

3. There will always be some 'give' on the side of the train, even if you have to go to a microscopic level to find it. So if the fly hits the glass of the train, it is not hitting all of the train and will not impact on the total speed of the train. On a tiny level the glass will give a little allowing a super-fast slow down - imagine the atoms of the train's glass bowing inwards very slightly to allow for the reduction in acceleration - as soon as the energy of the acceleration is dissipated - again at super-fast speed, the glass-atoms will reurn to their normal shape - move outwards. The other atoms of the fly surrounding the ones that impacted with the glass-atoms will also slow and they will move side ways dissipating their energy that way.

Answer 13

i think that the fly would go 0mph as soon as it hits the train. thats actually a good question little confusing but good.

Answer 14

Yeah.  And the last thing that went through the fly's mind was his butt.

Answer 15

This is all about Relative speed and mass. The fly is traveling at 5mph and has a mass of less than a gram. The train is traveling at 100mph and has a mass in excess of 1000 tons. At the moment of impact the force of the fly exerted on the train will be velocity x mass and the train will be again velocity x mass.

Without using exact figures the force of the fly will make no difference to the force of the train and therefore will result in no difference to the velocity of the train.

Hope this helps.

Answer 16

U better stop the pills man

Answer 17

train is travelling at 100 mph and fly at 5 mph(opposite direction) hence the impact is actually 100+5=105 mph.

Further, a car travelling at 120 mph hits another vehicle, coming from opposite direction, which is at 100 mph, then impact is 120+100  = 220 mph. If same applied in reverse, that is car at 120 mph hitting another speeding at 100 mph from behind then the impact is 120 - 100 = 20 mph. Result is less damage.