Question

Vectors have magnitudes 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
and (c) 7 unit.
​

Answer 1

Answer:

|a|−→=3

& ∣∣∣b→∣∣∣=4

(a). If R= 1 unit

then 32+42+2.3.4cos(θ)−−−−−−−−−−−−−−−−−√=1

→25+24cos(θ)=1

→24cosθ=−24

→cosθ=−1

→θ=1800

(b).32+42+2.3.4cosθ−−−−−−−−−−−−−−−−√=7

→25+24cosθ=49

→24cosθ=24

→cosθ=1

→θ=cos−1(1)=0∘

Hence angle between them is