Laws Of Motion Question 79
Question: The resultant of two forces $ 3P $ and $ 2P $ is R. If the first force is doubled then the resultant is also doubled. The angle between the two forces is[KCET 2001]
Options:
A) $ {{60}^{r}} $
B) $ 120^{o} $
C) $ 70^{o} $
D) $ 180^{o} $
Show Answer
Answer:
Correct Answer: B
Solution:
$ R^{2}={{(3P)}^{2}}+{{(2P)}^{2}}+2\times 3P\times 2P\times \cos \theta $ -(i) $ {{(2R)}^{2}}={{(6P)}^{2}}+{{(2P)}^{2}}+2\times 6P\times 2P\times \cos \theta $ -(ii) by solving (i) and (ii), $ \cos \theta =-1/2 $
therefore $ \theta =120{}^\circ $
