Question

Two vectors have magnitues 3 unit and 4 unit respectively. What should be the angle between them if the magnitude of the resultant is (a) 1 unit ,(b) 5 unit , (c) 7 unit​

Answer 1

Answer:

(a) 180° (b) 90° (c) 0°

Explanation:

A = 3u B = 4u

R^2 = A^2+B^2+2ABcos@

for R= 1u

1^2 = 3^2+4^2+2×3×4×cos@

cos@ = -24/24= -1

hence @= 180°

now, for R= 5u

5^2 = 3^2+4^2+2×3×4×cos@

cos@ = 0/24= 0

hence @= 90°

again R= 7u

7^2 = 3^2+4^2+2×3×4×cos@

cos@ = 24/24=1

hence @= 0°