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} $

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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 $



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