# HELPPPPPPPPPP PLSSSSSS - Forces Multiple Choice

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#1
Hi I am really confused on how to tackle this multiple choice question. None of it makes any sense to me.

Two forces of 6N and 10N act a point. which of the following could not be the magnitude of the result?

A - 16N
B- 8 N
C-5N
D - 3N

The answer is D but I do not know why.

Any help would be appreciated.

Thank you

GG16
1
4 years ago
#2
(Original post by GG16)
Hi I am really confused on how to tackle this multiple choice question. None of it makes any sense to me.

Two forces of 6N and 10N act a point. which of the following could not be the magnitude of the result?

A - 16N
B- 8 N
C-5N
D - 3N

The answer is D but I do not know why.

Any help would be appreciated.

Thank you

GG16
Given two forces acting at a point, the maximum their resultant can be is the sum of the forces and the minimum is the difference of the forces.

I don't know about Physics courses to know if this is a fact you need to learn. What level of Physics are you doing?

If you're familiar with vector triangles then two forces and their resultant form a triangle and you can derive the two facts above by considering the triangle inequality.
1
4 years ago
#3
(Original post by GG16)
...
(Original post by Notnek)
... you can derive the two facts ...
Forces x, y, R > 0, define x to act upward, 0° <= @ <= 90°:

1) Vert comps oppose:
R^2 = (x - [email protected])^2 + ([email protected])^2
R^2 = ([email protected])^2 + ([email protected])^2 + x^2 - [email protected]
R^2 = y^2 + x^2 - [email protected]

2) Vert comps reinforce:
R^2 = (x + [email protected])^2 + ([email protected])^2
R^2 = y^2 + x^2 + [email protected]

@ = 0° => R_min via 1), R_max via 2):
(R_min)^2 = y^2 + x^2 - 2xy = (y - x)^2 => R_min = |y - x|
(R_max)^2 = y^2 + x^2 + 2xy = (y + x)^2 => R_max = y + x

So: |y - x| <= R <= y + x
0
5 months ago
#4
(Original post by GG16)
Hi I am really confused on how to tackle this multiple choice question. None of it makes any sense to me.

Two forces of 6N and 10N act a point. which of the following could not be the magnitude of the result?

A - 16N
B- 8 N
C-5N
D - 3N

The answer is D but I do not know why.

Any help would be appreciated.

Thank you

GG16
The minimum resultant force will be when the forces are acting in opposite directions and will be 4N (10-6). Therefore it cannot be 3N as this is less than the minimum resultant force and thus the answer is D.
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