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M1 Maths Question

am struggling with this question. When I do it by adding the vectors I get the correct answer but when I do it by finding the magnitude and angles of the forces like most questions require you to do I get the wrong answer. I just don't understand where I'm going wrong as it should be the same answer. Can someone help me please. I have attached the question and both methods.
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You worked out the angle of thrust using 27 rather than 24. wee slip there in the first part of solution.
(edited 7 years ago)
Original post by Neil Capelli
am struggling with this question. When I do it by adding the vectors I get the correct answer but when I do it by finding the magnitude and angles of the forces like most questions require you to do I get the wrong answer. I just don't understand where I'm going wrong as it should be the same answer. Can someone help me please. I have attached the question and both methods.


When you are given a force with magnitude X and some angle, when you resolve components you are finding the horizontal and vertical components (which you can express in vector form and is what the question has given you)


What you've done by using a method to answer a question that it isn't really asking is to take the horizontal and vertical components (eg the -19.2 14.4 which is the horizontal and vertical components of some force that you don't know the resultant of and don't need to), turn them into a resultant force (your 24) and the angle and then decomposing them to (theoretically) end up with -19.2 and 14.4 again.. so your working is like building a house with materials and then carefully deconstructing it because you need the materials, basically.

The way forward is ONLY to combine the vectors, which is what you would do if you were given 24 and the angle and then break it down.You ould see this if you hadn't gone wrong in your working somewhere.

In your working you have unfortunately swapped a 24 for a 27 and followed through with that in your initial diagram.
(edited 7 years ago)
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Neil Capelli
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Original post by mathcoachni
You worked out the angle of thrust using 27 rather than 24. wee slip there in the first part of solution.


Thanks so much!! That was a silly mistake!
Reply 4
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Neil Capelli
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Sean FM do you know what I need to do here also? I've done a-b but I'm completely stuck with parts c-f. Many thanks in advance!
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