Vector vector A has a magnitude of 27 units and points in the positive y-direction. When vector vector B is added to vector A , the resultant vector vector A + vector B points in the negative y-direction with a magnitude of 18 units. Find the magnitude of vector B ?
Since both is in y-axis (+ and -) you can use the magnitude of the resultant as the sum of the magnitudes of the two vectors A and B. (from Maazul H)
A= 27 units
A+B= 18 units (- y-axis)
27+B= -18 units (+ y-axis)
The magnitude of vector B is 45 units