Resultant of two forces p and q
The resultant of two forces p and q, such that p > q, acting along the same straight line but in opposite directions can be determined using the principles of vector addition.

Vector addition of forces p and q
When two forces act along the same line but in opposite directions, the resultant force is given by the difference between the two forces. In this case, the resultant force R can be calculated as R = p - q.

Determination of the resultant force
To determine the magnitude and direction of the resultant force, we need to subtract the smaller force q from the larger force p. If p > q, then the resultant force will act in the direction of the larger force (p) with a magnitude equal to the difference between the two forces (p - q).

Example
For example, if force p has a magnitude of 10 N and force q has a magnitude of 5 N, then the resultant force R will be 10 N - 5 N = 5 N. The resultant force R will act in the direction of force p with a magnitude of 5 N.

Conclusion
In conclusion, when two forces p and q act along the same straight line but in opposite directions, the resultant force can be determined by subtracting the smaller force from the larger force. The resultant force will act in the direction of the larger force with a magnitude equal to the difference between the two forces.