Question

An aeroplane leaves the airport and flies due north at a speed of 600 km/hr. At the same time, another aeroplane leaves the same airport and flies due west at a speed of 800 km/hr. What will be the distance between two planes after 1 hour?

• A. 120 km
• B. 100 km
• C. 80 km
• D. 110 km

Answer 1

The correct option is B

100 km

Let point O be the airport

Flight B moves towards the north at a speed of 600 km/hr

Fight A moves towards the west at a speed of 800 km/hr

Distance $OA=800\times 1=800km$

Distance $OB=600\times 1=600km$

Distance between the flight after 1 hour = AB

Applying pythagoras theorem in triangle AOB

$A{B}^2=O{A}^2+O{B}^2$

$A{B}^2=(800{)}^2+(600{)}^2$

$A{B}^2=6400+3600$

$A{B}^2=10000$

AB =100 km