The correct answer
would be letter d, 8.3.
Solution for the
problem follows:
Given are:
B = 6i - 8j
A is unknown; let A be = mi + nj
A+B is along the x axis (therefore A+B = Ki + 0j, where K is unknown,
but then again the
magnitude of A+B is the similar as the magnitude of A,
so
mag(A+B)=K=sqrt(m^2+n^2), or K^2 = m^2+n^2.
A+B, from simple vector addition, will be now (m+6)i + (n-8)j.
Ever since we previously
know A+B = Ki + 0j, we now know that:
m+6 = K
n-8 = 0, which implies n=8.
Thus, K^2=m^2+n^2 ====> (m+6)^2 = m^2 +8^2
= m^2 + 12m + 36 = m^2 + 64
= 12m = 28
= m = 2.33333...
Therefore, the magnitude of A is sqrt[(2.333...)^2 + 8^2] = 8.3333
