# Finding Mechanics question hard

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Thread starter 4 weeks ago
#1
Three forces of sizes 15 N, 7 N and 19 N pulling at 120° to each other are acting on a particle
Find:
a) The size of the resultant force
b) The direction of the resultant force to the 19N force
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4 weeks ago
#2
Convert each force into a vector (of lengths 19, 7 and 15, but bearings 0, 120,240 degrees), then add the vectors to get the resultant vector.
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Thread starter 4 weeks ago
#3
(Original post by DFranklin)
Convert each force into a vector (of lengths 19, 7 and 15, but bearings 0, 120,240 degrees), then add the vectors to get the resultant vector.
Thanks for replying so soon.

I'm finding it difficult to understand without drawing a diagram, but I can't do that either. So which vectors do you add?
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4 weeks ago
#4
(Original post by alfiethfc02)
Three forces of sizes 15 N, 7 N and 19 N pulling at 120° to each other are acting on a particle
Find:
a) The size of the resultant force
b) The direction of the resultant force to the 19N force
Draw a diagram - have you been taught how to resolve forces?
0
4 weeks ago
#5
(Original post by DFranklin)
Convert each force into a vector (of lengths 19, 7 and 15, but bearings 0, 120,240 degrees), then add the vectors to get the resultant vector.
Unlikely to have been taught this yet ...
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Thread starter 4 weeks ago
#6
(Original post by Muttley79)
Draw a diagram - have you been taught how to resolve forces?
We have, but I'm unsure as to which direction you resolve.
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4 weeks ago
#7
(Original post by alfiethfc02)
We have, but I'm unsure as to which direction you resolve.
So pick one force to act up the paper say 19N, then draw a line 120 to that (15N) then the third at 240 to the first (7N) [I picked 19N to go up the page because of the second part]

Now an equivalent system will be a force P acting on a bearing theta.

Resolve vert for the three forces and put equal to Pcos theta

Repeat horiz and put equal to .... [have a guess]
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Thread starter 4 weeks ago
#8
(Original post by Muttley79)
So pick one force to act up the paper say 19N, then draw a line 120 to that (15N) then the third at 240 to the first (7N) [I picked 19N to go up the page because of the second part]

Now an equivalent system will be a force P acting on a bearing theta.

Resolve vert for the three forces and put equal to Pcos theta

Repeat horiz and put equal to .... [have a guess]
I got 5.1N and 40 degrees...but apparently this is wrong. Could anybody please explain?
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4 weeks ago
#9
(Original post by alfiethfc02)
I got 5.1N and 40 degrees...but apparently this is wrong. Could anybody please explain?
Post your working - we can't do questions for you.
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