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# m1 vectors question

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1. Can someone explain part a please?
what i thought was F1 + F2 = F3, but it is wrong
2. (Original post by alesha98)

Can someone explain part a please?
what i thought was F1 + F2 = F3, but it is wrong
F1 + F2 = F3

This would be if F3 was the resultant of F1 and F2. But that's not what the question says.

Instead, if three forces are in equilibrium then their resultant is 0. So you should have

F1 + F2 + F3 = 0.
3. (Original post by notnek)
F1 + F2 = F3

This would be if F3 was the resultant of F1 and F2. But that's not what the question says.

Instead, if three forces are in equilibrium then their resultant is 0. So you should have

F1 + F2 + F3 = 0.
so in equilibrium, all forces added together are equal to 0?
4. If you imagine that F1 and F2 will make a resultant force, F3 will be the same as that resultant force but 180 degrees opposite so it cancels out and therefore in equilibrium
5. (Original post by alesha98)
so in equilibrium, all forces added together are equal to 0?
Yes.
6. (Original post by notnek)
Yes.
When a particle rests on a horizontal ground, in equilibrium, i do:
R-mg=0 but not R+mg =0.
So i am still confused of the concept that in equilibrium, all forces added together are equal 0?
7. (Original post by alesha98)
When a particle rests on a horizontal ground, in equilibrium, i do:
R-mg=0 but not R+mg =0.
So i am still confused of the concept that in equilibrium, all forces added together are equal 0?
If you take upwards as positive then expressed as vectors we have the reaction equal to +R and the weight equal to -mg where mg is the magnitude of the weight and it has negative direction.

If you sum these forces you get zero:

R + (-mg) = 0

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