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Edexcel M1 Chapter 4 Ex 4a

Is there anyone that can help me please? I am on question 9 and really struggling to understand how to get the answer to part c. I understand how to resolve the forces in the x and y direction which is parts a and b but in C it wants me to find the magnitude of the unknown forces P and Q but I honestly dont understand how to get the answer. The diagram is below and I was hoping that somebody would help me understand what I need to do. Thanks :smile:
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Reply 1
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BabyMaths
Resolving vertically: Q sin 45 + P sin 30 = 4 + 8 sin 45

Resolving horizontally: .....
Reply 2
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NinjaChloe
OP
I understood how to resolve the forces and that part, I just dont know how I use that to then find P and Q. :frown: can you help me please?
Reply 3
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BabyMaths
Write out the other equation a solve the simultaneous equations.
Reply 4
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NinjaChloe
OP
How do you do that?? Wouldnt the equations be different with the subjects?? Im sorry but I dont understand.
Reply 5
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BabyMaths
Resolving vertically: Q sin 45 + P sin 30 = 4 + 8 sin 45

Resolving horizontally: 8 cos 45 + Q cos 45 = P cos 30

Q sin 45 + P sin 30 = 4 + 8 sin 45

Q cos 45 - P cos 30 = -8 cos 45
Reply 6
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NinjaChloe
OP
Would the two q values cancel each other out because they are the same value??
Reply 7
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BabyMaths
Original post by NinjaChloe
Would the two q values cancel each other out because they are the same value??


If you subtract one equation from the other you will eliminate the Q and obtain an equation which will give you the value of P.
Reply 8
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NinjaChloe
OP
Thankyou for telling me how to do it. Can I ask you one more thing though?? Why does it have to be done in simeultaneous equations?? Sorry for probably sounding dumb, but thankyou for helping me :smile:
Reply 9
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BabyMaths
You have two unknowns in each equation, if you only look at one equation at a time you will not be able to pin it down to particular values of P and Q.

Don't worry about sounding dumb. People here generally don't mind where you're up to with your maths, as long as you make an effort and show that you're making an effort.
Reply 10
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NinjaChloe
OP
I think I understand now. Thankyou so much, I wouldnt have gotten anywhere without you :smile: and its good to know that I dont sound too dumb :biggrin:

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