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Maths, Addmaths and Statistics: Post your doubts here!

AhsanAfzal

AhsanAfzal

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Saad Mughal said:
The Resultant Velocity, i.e. Vp = Distance/Time = 240i + 100j.
The formula is Vp = Vp/q + Vq.
Just rearrange the formula,
Vp/w = Vp - Vw = 240i + 100j + 60i - 60j = 300i + 40j.
Hope that helps. :)
Click to expand...
isn't V(p) the velocity in still air in the formula?
 
Saad Mughal

Saad Mughal

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AhsanAfzal said:
there was another question before this pls answer that too. thnks in advance :)
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Saad Mughal said:
(i) The velocity vector is in the form (xi +yj).
The magnitude is given (10√2), this means that 10√2 = √x^2 +y^2.
The direction is north - east, this means that a angle of 45 deg. is subtended with both y-axis and x-axis (see diagram).
For calculating the component vectors, take trigonometric ratios.
cos 45 = x/10√2
x= 10
cos 45 = y/10√2
y = 10
Therefore, the velocity vector is (10i + 10j).

(ii) Position vector = Initial position vector + distance travelled.
= (-4i+8j) + 2(10i+10j) = 16i +28j.

(iii) V(p) = V(p/q) + V(q) [V(p) = Velocity of P, V(q) = Velocity of Q, V(p/q) = Velocity of P relative to Q].
V(p/q) = V(p) - V(q)
V(p/q) = (10i + 10j) - (8i + 6j) = 2i + 4j

(iv) When they meet, Position vector of P = Position vector of Q,
Hence,
(16i +28j) + t(10i+10j) = (19i + 34j) + t(8i + 6j) (Initial vector at 12 00 + Distance traveled in t hours).
Comparing coefficients of i,
16+10t = 19 +8t
2t = 3
t = 1.5 hours.
Time at which they meet = 12 00 + 1.30 = 13 30 hours.

Position vector at that time (take either of the two) = (16i + 28j) + 1.5(10i + 10j)
Position vector at that time (take either of the two) = 16i + 28j + 15i +15j = 31i + 43j.

Hope that helps! :)

View attachment 24140
Click to expand...
I replied to a similar question to you last time around. Please check it. This will be done in the same way. :)
 
Suchal Riaz

Suchal Riaz

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AhsanAfzal said:
So the mArking scheme is wrong? examiner report also says that we have to subtract and addition was common mistake.
Click to expand...

Saad Mughal said:
The Resultant Velocity, i.e. Vp = Distance/Time = 240i + 100j.
The formula is Vp = Vp/q + Vq.
Just rearrange the formula,
Vp/w = Vp - Vw = 240i + 100j + 60i - 60j = 300i + 40j.
Hope that helps. :)
Click to expand...

oops i did not see that. i thought that maybe u r using the correct formula so ur answer will be correct :confused:
 
Suchal Riaz

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AhsanAfzal said:
ohh got it. i thought true velocity means the velocity in still air.
Click to expand...

true velocity is velocity as seems compared to ground or earth or a man standing on earth.
magnitude of velocity of airplane for example is 400km/h but the wind can change how it actually travels. for example velocity of air is 20km/h in direction as opposite of airplane, then i will think, as standing on ground, that the plane is travelling at 380km/h. so compared to earth true velocity is 380 but compared to wind the speed of place is still 400km/h. to make the velocity of airplace actually 400km/h the velcity of air should be 0. so thats why they call it 'in still air' so we translate it as V(a/w)=400km/h and the actual velocity (V(a/w)+V(w)) as true velocity.
i hope i did not confuse u further :p
 
AhsanAfzal

AhsanAfzal

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are there any notes on reltive velocity(including these i and j questions)? because it was not in the add maths book..
 
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