MyFishFinder Forum
The Fisherman's Wharf => OffTopic => Topic started by: rgfixit on Jul 30, 2022, 11:31 AM

If two cars are passing each other at 55 mph, is their combined speed at the point of intersection 110 mph.
( I was thinking about this this morning as I was going fishing)

Why wouldn't it be? What you smokin on?

N
If you are refering to them crashing head on, then no.
It's an E=MCsquared thing Bob.
Basically, if both cars are the same size and weight, it's like a car hitting an imoveable object (like a mountain).
However, since we are speaking about cars here, they would both colapse upon impact, absorbing some of the energy.
So there's tons of other variables involved.
Hence the crash tests the insurance companies have been doing since forever.
Almost impossible to "calculate" what happens in a crash.
Data!!!!
However, if you are saying they will pass each other, then the Delta S (speed) would indeed be 110 mph.
But only in relationship to each other, which is not typical.
Speed is typically measured in relationship to the ground, which is stationary.
Hope that helps.

I think you are talking about the situation where two cars impact each other head on. When thinking about velocity in these situations you have to think about "frame of reference". From the point of view of one of the drivers, the other driver is approaching at 110 mph. If one driver is traveling at 55mph (according to the speedometer) and is rear ended by another driver going 75 mph(according to the speedometer) then from the drivers perspective the impact occurs at (7555) = 20 mph.
There are videos online where a device propels a tennis ball at say 20 mph. A pickup truck goes 20 mph while a guy fires the device out the back of the truck, straight behind the truck as the truck passes through an intersection. From a camera on the ground, the ball just bounces straight up and down. From the perspective of the guy who fired the ball the ball is moving at 20 mph. Welcome to Einstein's world!

The question was what is the combined speed. 55+55=110

This is the smart butt in me, at the point of intersection at the time they are passing would be zero at that moment in time as the forces from each vehicle would counter act each other and be stationary for that split second. So the wind forces hitting each other would it stop each other, just the thoughts rolling through my head as I read each very thought out answer and just gets my brain thinking of all the possibilities.

So…my question was…
If two cars are passing each other at 55 mph, is their combined speed at the point of intersection ( meaning when they actually pass each other)110 mph.
It’s a trick question I think. But a simple answer.

Relative Speed.
“Relative” means “in comparison to”. Thus, the relative speed is used when two or more bodies moving with some speed are considered. To make things simpler, one body can be made stationary (i.e. Speed =zero) and take the speed of the other body with respect to the stationary body, which is the sum of the speed if the bodies are moving in the opposite direction and the difference if they are moving in the same direction. This speed of the moving body with respect to the stationary body is called the relative Speed.
So the answer to your question Bob, is “yes”, 110 mph.

You are correct! All velocity is relative.
The relative velocity of two cars traveling towards each other at 55 mph would be 110 mph.

All velocity is relative.
2nd last para of my first post