IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: T.Q on December 09, 2009, 01:15:16 pm
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Two forces, (4i – 5j) N and (pi + qj) N, act on a particle P of mass m kg. The resultant
of the two forces is R. Given that R acts in a direction which is parallel to the
vector (i – 2j),
(a) find the angle between R and the vector j,
(b) show that 2p + q + 3 = 0.
Given also that q = 1 and that P moves with an acceleration of magnitude 8?5 m s–2,
(c) find the value of m.
i need help in part (b) with explanation plz
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When i get home
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You need to realise that the resultant vector is parallel to i – 2j
This means that the resultant vector will have a magnitude of a multiple of Root 5 ( by finding the magnitude of i - 2j)
Anyways,
so to get a resultant force, you add your vectors
4i – 5j + pi + qj = Resultant
Because resultant is parallel to i - 2j, you know that the ratio of i's to j's are equal
therefore
(4+p)/(q-5) = 1/-2
Cross multiply
-2(4-p) = q - 5
-8 - 2p = q - 5
2p + q + 3 = 0
:)
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Thannnnnnnnnksss vanibharutham !! :D
What a coincidence!
I was going to ask my teacher tomorrow about dat problem
-
You need to realise that the resultant vector is parallel to i – 2j
This means that the resultant vector will have a magnitude of a multiple of Root 5 ( by finding the magnitude of i - 2j)
Anyways,
so to get a resultant force, you add your vectors
4i – 5j + pi + qj = Resultant
Because resultant is parallel to i - 2j, you know that the ratio of i's to j's are equal
therefore
(4+p)/(q-5) = 1/-2
Cross multiply
-2(4-p) = q - 5
-8 - 2p = q - 5
2p + q + 3 = 0
:)
thank you very much :)