When three forces act on an object, their sizes are 7n, 8N and 9N respectively. What is the resultant force? The answer is a 0n B 7n C 15N D 25N If you know, please write down the answers and reasoning! How can three or more forces determine the value range of resultant force?

When three forces act on an object, their sizes are 7n, 8N and 9N respectively. What is the resultant force? The answer is a 0n B 7n C 15N D 25N If you know, please write down the answers and reasoning! How can three or more forces determine the value range of resultant force?

Let's start with the minimum
The minimum value of the resultant force of the three forces in an unfixed direction is determined by whether the line segments representing the magnitude of the three forces can form a triangle
If a triangle can be formed (that is, the sum of any two line segments is greater than the third line segment), then the sum of the three vectors may return to the origin (that is, the resultant force is zero)
If a triangle can not be formed (that is, the length of one line segment is greater than the sum of the other two lines), then the reasonable minimum value is equal to the longest line segment minus the sum of the other two lines
From the condition of this question, we can know that: 7 + 8 is greater than 9; 8 + 9 is greater than 7; 7 + 9 is greater than 8. So the three line segments representing the size of three forces can form a triangle, so it is possible for the three vectors to add up and return to the origin, so the reasonable minimum value can be zero
Maximum value:
When the three forces are in the same direction, the resultant force is the largest,
Because 7 + 8 + 9 = 24
So the maximum of the resultant force is 24
So: A, B, C are correct