Addition of Vectors (Qns.& Ans) V.S.A.Q.’S (2 marks)
Addition of Vectors Addition of Vectors: These solutions were designed by the ‘Basics in Maths’ team. These notes are to help intermediate First-year Maths students. Inter Maths – 1A two-mark questions and solutions are very useful in IPE examinations. Addition of Vectors QUESTION 1 Find the unit vector in the direction of Sol: Given vector is The unit vector in the direction of a vector is given by QUESTION 2 Find a vector in the direction of a where that has a magnitude of 7 units. Sol: Given vector is The unit vector in the direction of a vector is The vector having the magnitude 7 and in the direction of is QUESTION 3 Find the unit vector in the direction of the sum of the vectors, a = 2i + 2j – 5k and b = 2i + j + 3k Sol Given vectors are a = 2i + 2j – 5k and b = 2i + j + 3k a + b = (2i + 2j – 5k) + (2i + j + 3k) = 4i + 3j – 2k QUESTION 4 Write the direction cosines of the vector Sol: Given vector is ∴ Direction cosines are QUESTION 5 Show that the points whose position vectors are – 2a + 3b + 5c, a + 2b + 3c, 7 a – c are collinear when a, b, c are non-collinear vectors Sol: Let OA = – 2a + 3b + 5c, OB = a + 2b + 3c, OC = 7 a – cA B = OB – OA = a + 2b + 3c – (– 2a + 3b + 5c) AB = 3a – b – 2c AC = OC – OA = 7 a – c – (– 2a + 3b + 5c) AC = 9a – 3b – 6c = 3(3a – b – 2c) AC = 3 AB A, B and C are collinear QUESTION 6 ABCD is a parallelogram if L and M are middle points of BC and CD. Then find (i) AL and AM in terms of AB and AD (ii) 𝛌, if AM = 𝛌 AD – LM Sol: Given, ABCD is a parallelogram and L and M are middle points of BC and CD (i) Take A as the origin M is the midpoint of CD AM = = AD + ½ AB (∵ AB = DC) L is the midpoint of BC AL = = AB + ½ AD ((∵ BC = AD) (ii) AM = 𝛌 AD – LM AM + LM= 𝛌 AD AD + ½ AB + AD + ½ AB – (AB + ½ AD) = 𝛌 AD AD + ½ AB + AD + ½ AB – AB – ½ AD = 𝛌 AD 3/2 AD = 𝛌 AD ∴𝛌 = 3/2 QUESTION 7 If G is the centroid of the triangle ABC, then show that OG = when, are the position vectors of the vertices of triangle ABC. Sol: OA = a, OB = b, OC = c and OD = d D is the midpoint of BC OD = G divides median AD in the ratio 2: 1 OG = ∴ OG = QUESTION 8 If = , = are collinear vectors, then find m and n. Sol: Given , are collinear vectors ⟹ = λ Equating like vectors 2 = 4 λ; 5 = m λ; 1 = n λ λ = 5 = m ⟹ m =10 1 = n ⟹ n = 2 ∴ m = 10, n = 2 QUESTION 9 Let If , . Find the unit vector in the direction of a + b. Sol: Given vectors are and a + b = The unit vector in the direction of a + b = = = QUESTION 10 If the vectors – 3i + 4j + λk and μi + 8j + 6k. are collinear vectors, then find λ and μ. Sol: let a = – 3i + 4j + λk, b = μi + 8j + 6k ⟹ a = tb – 3i + 4j + λk = t (μi + 8j + 6k) – 3i + 4j + λk = μt i + 8t j + 6t k Equating like vectors – 3 = μt; 4 = 8t, λ = 6t 4 = 8t t = – 3 = μ ⟹μ=– 6 λ = 6 ⟹ λ = 3 ∴ μ=– 6, λ = 3 QUESTION 11 ABCD is a pentagon. If the sum of the vectors AB, AE, BC, DC, ED and AC is 𝛌 AC then find the value of 𝛌 Sol: Given, ABCD is a pentagon AB + AE + BC + + DC + ED + AC = 𝛌 AC (AB + BC) + (AE + DC + ED) + AC = 𝛌 AC AC + AC + AC = 𝛌 AC 3 AC = 𝛌 AC 𝛌 = 3 QUESTION 12 If the position vectors of the points A, B and C are – 2i + j – k and –4i + 2j + 2k and 6i – 3j – 13k respectively and AB = 𝛌 AC, then find the value of 𝛌 Sol: Given, OA = – 2i + j – k , OB = –4i + 2j + 2k and OC = 6i – 3j – 13k AB = OB – OA = –4i + 2j + 2k – (– 2i + j – k) = –4i + 2j + 2k +2i – j + k = –2i + j + 3k AC = OC – OA = 6i – 3j – 13k – (– 2i + j – k) = 6i – 3j – 13k +2i – j +
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