physics

你有冇check 吓條問題呀?
有兩個ans wor
一係A. 0N,一係C. 4N
3N同4N 有3個情況ge
3+4=:
1)7N (maximum value when 3+4 are in the same direction ) 意思係3N向左,4N再向左,咁就有7N
2)1N OR -1N (minimum value when 3+4 are in the opposite direction)意思係3N向左,4N向右, 咁相差會有1N ge (-1N 係depends on 你個方向)
3)5N (when 3+4are at right angle)意思係畢氏定理咁,長4N(3N) 同高係3N(4N),咁個斜邊係5N lo

so A.0N 同C.4N 都係ANS= =

The answer is A.
B is wrong because resultant force is 1 N when they are anti- parallel.
C is wrong because resultant force can be 4 N when this three forces
forms a isosceles triangle (等腰三角形) where 4-N force and
the resultant force are the isosceles side.
D is wrong because resultant force is 7 N when they are parallel and in
same direction.