Question

A vector A is directed along x-axis is to be added to vector B which has a magnitude of 7.0m.The sum is a third vector which is directed along y-axis with a magnitude that is 3.0 times of vector A. What is that magnitude of A?

Answer 1

Answer:

Let magnitude of vector A = x

Given that resultant of A+B is in positive y direction with 3x magnitude, hence B must be = -xi + 3xj

magnitude of B is also given as 7, hence

magnitude of B =  √(x^2 +9x^2) = 7

√10 x =7

x = 7/√10 Ans

Explanation: see the attached drawing you can understand. Always try to break vectors in x-y directions and then balance/equate.