Three coplanar forces $F_1$, $F_2$ and $F_3$ act on a point object - AQA - A-Level Physics - Question 20 - 2018 - Paper 1

To determine which combination of forces cannot produce a resultant force of zero, we need to analyze the options based on vector addition. The resultant force can equal zero if the vector sum of the forces is zero.

1. For option A:

   • $F_1 = 3 N$, $F_2 = 4 N$, $F_3 = 5 N$.
   • The resultant can be $3 + 4 - 5 = 2 N$; hence, it can reach zero under certain arrangements.

2. For option B:

   • $F_1 = 8 N$, $F_2 = 8 N$, $F_3 = 8 N$.
   • All forces are equal and directed, so the resultant cannot be zero.

3. For option C:

   • $F_1 = 2 N$, $F_2 = 10 N$, $F_3 = 10 N$.
   • With these values, it is possible to have zero resultant through appropriate direction adjustments.

4. For option D:

   • $F_1 = 6 N$, $F_2 = 6 N$, $F_3 = 10 N$.
   • This combination can allow for a zero resultant as well, depending on orientation.

Thus, the combination of forces in option B (8, 8, and 8) can never produce a resultant force of zero, as they are entirely aligned and will always sum to 24 N.