LostinNY wrote:

Hi Franz, I understand that when two objects are coming towards each other you add up the quantities but I still dont understand how 25 meters in 1 second is the same as 90 kmh"

V+40 yes understood - sorry if its an easy question but I'm just not seeing it clearly!

Okay I'm going to try to type it out in a long winded way, but hopefully it makes sense

First thing you want to do is get similar units. So..

\(\frac{75m}{3secs} *\frac{60sec}{1min} *\frac{60 mins}{1 hr} * \frac{1km}{1000m} = \frac{90km}{hr}\)

this is how i learned it in physics, its long, but its simple and helps eliminate any mistakes. All I'm doing is multiplying \(\frac{75m}{3secs}\)by 1 over and over again.

i.e. \(\frac{60sec}{1min} = 1\)

In the end the undesirable units in the numerator and denominator cancel out and you're left with km/hr... Which is what you're looking for.