19. The magnitude of a vector cannot be:
P) unity
2) positive
3) negative
4) zero
20. Three concurrent coplanar forces are given in the following options. Which one does not give a zero tesultant?
1) \( 3 \mathrm{~N}, 4 \mathrm{~N} \& 5 \mathrm{~N} \)
2) \( 10 \mathrm{~N}, 10 \mathrm{~N} \& 10 \mathrm{~N} \)
3) \( 10 \mathrm{~N}, 10 \mathrm{~N} \& 3 \mathrm{~N} \)
(4) \( 4 \mathrm{~N}, 8 \mathrm{~N} \& 15 \mathrm{~N} \)
21. Angle that the vector \( \overline{\mathrm{a}}=2 \hat{i}+3 \hat{j} \) makes with \( Y \) axis is :
1) \( \tan ^{-1}\left(\frac{3}{2}\right) \)
2) \( \tan ^{-1}\left(\frac{2}{3}\right) \)
3) \( \sin ^{-1}\left(\frac{2}{3}\right) \)
4) \( \cos ^{-1}\left(\frac{3}{2}\right) \)
