Question 43142:  Two planes leave an airport at the same time, one flying due west at 500km/h and the other flying due southeast at 300km/h. What is the distance between the planes two hours later? 
 Answer by psbhowmick(878)      (Show Source): 
You can  put this solution on YOUR website! Note: Distance = Speed x Time
 
 
In 2 hours, the plane travelling to West travels a distance of 500x2 = 1000 km. 
In 2 hours, the plane travelling to South-East travels a distance of 300x2 = 600 km.
 
 
If their initial position was the point O then their final positions, after 2 hours, are points A and B respectively. 
 
 
 
We need to know the length of AB. 
In triangle BCO,  as OB is in South-East direction. 
So,   = cos(< BOC) =   
or   
or   
or   
or    
or OC = 424.264 km
 
 
Therefore, AC = AO + OC = 1000 + 424.264 = 1424.264 km
 
 
As BCO is a right angled isosceles triangle with 
 
Now, in triangle ACB, 
Applying Pythagorus theorem, 
  
or   
or   
or   
or AB = 1486.112 km
 
 
Hence, the reqd. distance between the two planes after 2 hours is 1486.112 km. 
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