M1 Mechanics Vectors Help D:

Ahh~ i've been stuck on this question for like an hour now trying different methods and constantly getting the wrong answer; i was wondering if anyone could help me with this and talk me through how to do it? ^^"

Thanks :biggrin:

At 11:00 hours the position vector of an aircraft relative to an airport O is (200i + 30j) km, i and j being unit vectors due east and due north respectively. The velocity of the aircraft is (180i - 120j) km/h.

Find the time when the aircraft is due east of the airport O

(edited 12 years ago)

Reply 1

Gemini92

Original post by Bakasplitz

Ahh~ i've been stuck on this question for like an hour now trying different methods and constantly getting the wrong answer; i was wondering if anyone could help me with this and talk me through how to do it? ^^"

Thanks :biggrin:

At 11:00 hours the position vector of an aircraft relative to an airport O is (200i + 30j) km, i and j being unit vectors due east and due north respectively. The velocity of the aircraft is (180i + 120j) km/h.

Find the time when the aircraft is due east of the airport O

Ignore the i component (the east one) and just use the j component (the north component). You have the position and the speed, so you need to work out when the plane is due east of the airport and this occurs when the j component of the position of the plane is 0. Once you have the time taken for the plane to become due east, you can work out the time that this occurs by adding 11 hours to it.

Reply 2

In One Ear

18

For this problem to be solvable shouldn't the j component of the aircraft's velocity be negative? Else the aircraft will never be due east of the airport...

Reply 3

Bakasplitz

OP

10

Original post by Gemini92

Ignore the i component (the east one) and just use the j component (the north component). You have the position and the speed, so you need to work out when the plane is due east of the airport and this occurs when the j component of the position of the plane is 0. Once you have the time taken for the plane to become due east, you can work out the time that this occurs by adding 11 hours to it.

just completed it, now i can do the rest of the question :biggrin:

thanks so much ^^"

Reply 4

Bakasplitz

OP

10

Original post by In One Ear

For this problem to be solvable shouldn't the j component of the aircraft's velocity be negative? Else the aircraft will never be due east of the airport...