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M1 Combining forces

Each of two forces has magnitude X N, and the resultant of these two forces has magnitude 12 N. When the magnitude of one of the forces is increased by 70%, the magnitude of the resultant of the two forces becomes 21N. Find X and the angle between the two forces.


I really have no idea what to do here. Completely stuck. Help appreciated.
Diagram would be useful.

Apply the cosine rule in each case to get two simultaneous equations.
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Julii92
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Original post by ghostwalker
Diagram would be useful.

Apply the cosine rule in each case to get two simultaneous equations.


Thanks! I drew a few diagrams but didn't think to use the cosine rule.

In an exam, would it matter whether I chose to answer a question by constructing a force diagram or by splitting and combining components (if the question doesn't explicitly state which method to use)?

Or is this something which would depend on the board?
Original post by Julii92

In an exam, would it matter whether I chose to answer a question by constructing a force diagram or by splitting and combining components (if the question doesn't explicitly state which method to use)?

Or is this something which would depend on the board?


Years since I did A-levels, so can't give a definitive answer.

But, it seems reasonable that you can use what ever method you like, if the paper doesn't specify.

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