Another Brain Tease

Post by **kazbah** » Mon Nov 28, 2005 10:23 am

Just cos I can...

If a car is traveling at 100 km/h and there is a fly in the car what speed is the fly flying at? It it

a) 100 km/h
b) 100 km/h plus the speed he is flying at
c) just the speed he is flying at
d) who gives a rats

afterburner · Post by **afterburner** » Mon Nov 28, 2005 10:58 am

Which direction is the fly flying in?

ahew · Post by **ahew** » Mon Nov 28, 2005 11:04 am

crap.. not another physics question. hahahahahaha i've got a 2 to 1 vote against me on the other thread already.

ok... this one is not as bad though. The speed is relative to where you are. If you were in the car, the answer would be c).

If you were out of the car stationary on the road, the answer is b)

Or for other people reading my post d) and then followed by abuse.

edit: doesn't matter which direction if it's in 2D it will be - or + depending if it's with or against the motion of the car. 3D is heaps trickier as it deals with vectors so "you don't wanna go there girlfriend".

scarecrow · Post by **scarecrow** » Mon Nov 28, 2005 11:11 am

The car becomes an inertial frame of reference, the answer is C to an observer within the car and to the fly.

If the car is accelerating then the fly would be flying with the magnitude of the cars acceleration + it's own speed

SchumieFan · Post by **SchumieFan** » Mon Nov 28, 2005 12:44 pm

cant we just lock this thread now???

Post by **kazbah** » Mon Nov 28, 2005 1:14 pm

SchumieFan wrote:cant we just lock this thread now???

Nah!

Post by **Supplanter** » Mon Nov 28, 2005 4:58 pm

SchumieFan wrote:cant we just lock this thread now???

Yes please

Slither · Post by **Slither** » Mon Nov 28, 2005 6:34 pm

Wasn't this an Einstein question?

I thought he came to the conclusion that it was C

Grue · Post by **Grue** » Tue Nov 29, 2005 11:08 am

Yup. Totally relative on whereabouts the observer is. You could go on forever - add the spin of the earth, etc.

A bullet fired from a car, to a stationary pedestian, is moving at CarSpeed+BulletSpeed. But photons from a car's headlights are only travelling at light-speed, not LightSpeed+CarSpeed.

Who's gunna start about mass and time-dialation with velocity?

mell · Post by **mell** » Tue Nov 29, 2005 7:44 pm

depends..........is it the speed of the fly relative to the observer...being u in the car....

or is it the speed of the fly relative to the road....if its relative to the road its speed of car plus speed of fly( if fly is moving)

if other its speed of fly relative to u.

yr 12 pyhsics did come in handy aye:):):)

Nacho · Post by **Nacho** » Wed Nov 30, 2005 8:04 am

It was an Einstein question involving a man moving on a train. However the question is that............

Is the fly affected by the inertial force not being in contact with the car? Was the fly ever in contact with the car at any point?