Relative motion problems?

Question

1.is a passenger in an aeroplane more concerned about the planes air speed(relative to the air) or its ground speed ( speed relative to the ground) why?

A film crew for a nature film is in a helicopter skimming just above the scrub in Northern Territory at a velocity relative to the ground 33 ms-1 S. suddenly the crew spots a mob of kangaroos 2km away heading south at an average speed of 13ms-1 relative to the ground

a) what is the velocity of the helicopter relative to the kangaroos

b) what is the velocity of the kangaroos relative to the helicopter

c) how long will it take the crew to reach the spot where the kangaroos where they were first seen?

d) how long after the first view of the kangaroos will the helicopter take to reach the mob?

Answer 1

1. It depends on the passenger's temperament i suppose. the more immediate problem is the air speed in terms of any problem with the plane. but if hes in a hurry its the ground speed. as the wind could be 200 mph and the plane's airspeed could be 200mph , but the plane would go nowhere(ground speed 0)

a. Assuming the helicopter is also heading south:

to do this imagine that the kagaroo is stationary and the entire earth and helicopter are moving. how fast would the helicopter then be moving if you were the kangaroo?

33-13 = 20m/s

b.

same in reverse:

13 - 33 = -20m/s (negative since kangaroos are moving in opposite direction relative to helicopter

c:

v = d/t so t = d/v = 2000/33 = 60.60s

d:

use the relative speed of the helicopter to the kangaroos and therefore take the kangaroos as stationary:

t = d/v = 2000/20 = 100s

Furthermore the answer to b is not 46 since that would give the kangaroos a velocity relative to the ground of 46 + 33. which isnt 13. if the velocity is 46 relative to the helicopter then the kangaroos are moving away from the helicopter at 46m/s. which for a start would mean that the helicopter would never catch them.

Answer 2

Do you believe anyone is going to spent\d his precious time solving this?

Answer 3

A: The velocity of the helicopter is 33 - 13 = 20 ms, because the Helicopter is headed towards the Kangaroos

B: The velocity of the kangaroos is 33 + 13 = 46 ms, because the Kangaroos are heading in the same direction.

C: It will take: 2000 M / 33 = 60.6 Seconds, It will take just over a minute to reach the point where the Kangaroos where first seen.

D: K = 13MS, H = 33 MS :::: So in the 60 seconds to reach the point where they were first seen, the Kangaroos will travel another 13(60) = 780 Meters, and In order to cover that distance again, the Helicopter will take 780/33 = 23 Seconds::

So it will take 23 Seconds after the first seen point to catch up with the mob.