an objects motion can change as a result of forces acting on it. which pair of forces acting on an object…

Explanation:

Step1: Calculate net - force for each pair

Net - force is calculated as the difference between the two forces when they act in opposite directions.

Step2: For the first pair

The forces are 10 N and 20 N. Net - force $F_1=|20 - 10|=10$ N.

Step3: For the second pair

The forces are 10 N and 15 N. Net - force $F_2=|15 - 10| = 5$ N.

Step4: For the third pair

The forces are 5 N and 20 N. Net - force $F_3=|20 - 5|=15$ N.

Step5: For the fourth pair

The forces are 15 N and 15 N. Net - force $F_4=|15 - 15| = 0$ N.

Step6: Compare net - forces

We have $F_4(0\text{ N})<F_2(5\text{ N})<F_1(10\text{ N})<F_3(15\text{ N})$.

Answer:

The pair of forces 5 N and 20 N will cause the greatest change in motion.