# Speed of Cars while running toward them

#### jonboy

If a car is coming directly toward me going 35 mph, and I am running 6 mph towards it, what speed from the observer in the car will it look like I am going?

This is not homework. I am reading a book on Einstein and his theory of relativity has caused me to think of this.

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#### werehk

PHF Hall of Fame
If a car is coming directly toward me going 35 mph, and I am running 6 mph towards it, what speed from the observer in the car will it look like I am going?

This is not homework. I am reading a book on Einstein and his theory of relativity has caused me to think of this.

That's really interesting. Suppose the car is travelling at a constant velocity, in fact, the one inside car would never know he is travelling at 35 mph and actually he has no means to know if he hasn't got an equipment for measurement. Prior to that, the windows of car should be masked so that observer cannot see what's happening outside. Then, if you are running towards the car, provided observer would not notice the background, the observer only notice you running towards him at a speed of 6 mph. The speed of car and you are all measured with reference to the earth, so if one is inside a system with constant velocity, observer would never notice that.

jonboy

#### topsquark

Forum Staff
If a car is coming directly toward me going 35 mph, and I am running 6 mph towards it, what speed from the observer in the car will it look like I am going?

This is not homework. I am reading a book on Einstein and his theory of relativity has caused me to think of this.
This was answered on our sister site: Math Help Forum. See here.

-Dan