[Julii92]

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.

[ghostwalker]

Diagram would be useful.

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

[Julii92]

(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?

[ghostwalker]

(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.