(CE) Phy Mechanics - Force

For this question, we can use triangle inequality.

That is, for any triangle with side x, y and z.

x + y >= z, y + z >= x, z + x >= y

For A, 3 + 4 = 7 > 6

4 + 6 = 10 > 3

3 + 6 = 9 > 4

So, this is possible.


圖片參考：http://i601.photobucket.com/albums/tt95/physicsworld9999/physicsworld01Jun040956.jpg?t=1244080639


For B, if the forces 2N and 4N are linear, then they can cancel out the 6N force. This is possible.


圖片參考：http://i601.photobucket.com/albums/tt95/physicsworld9999/physicsworld02Jun040956.jpg?t=1244080650


For C,

5 + 5 = 10 > 2

5 + 2 = 7 > 5

So, this is possible.


圖片參考：http://i601.photobucket.com/albums/tt95/physicsworld9999/physicsworld03Jun040956.jpg?t=1244080661


For D, 1 + 2 = 3 < 4

So, this is not possible

The answer is D.

ilovemadonna2009, I wanna ask, what if all the force acts on the body
horizontally upwards? Then all pairs are reasonable if the sum of force
is smaller that the weight of the object?