Relative motion problem?

Question

3. a jet aircraft has a speed relative to the air of 720km h-1 and that on a certain day the av wind velocity in aus is 40kmh-1 from the west. if a flight distance between perth and sydney is 4800km E how long will it take a jet to fly from

a)perth to sydney

b) sydney to perth

Answer 1

A: P --> SYDNEY

{

720 + 40 km/h tail wind so Net Speed : 760 Km/H

It will take 6.31 Hours to travel from Perth to Sydney

}

B: Sydney to Perth is A reversed so 720 - 40 = 680 Km/H

It will take 7.04 Hours to go from Sydney to Perth.

Answer 2

use simple resultant velocity. just add/subtract the speeds.

a) the west wind is a tailwind. resultant velocity is 760kn/hr.

therefore it takes 4800/760 = 6.32 hours (2 decimal places)

= 6 hrs 19 minutes (nearest min)

b) the west wind is a headwind. resultant velocity is 680km/hr.

therefore it takes 4800/680 = 7.06 hours (2 decimal places)

no vectors/pythagoras' theorem needed since you are travelling in straight lines with no diagonals involved.

= 7 hours 4 minutes (nearest min)