Answer:
The reason is because you and the truck are both moving at speeds relative to each other. Generally, when two bodies move in opposite directions to each other, one body appears to be moving faster relatives to the others frame of reference. A frame of reference can be simply described as an observer with a meter rule and a stop watch stationed to observe the motion or movement of another body.
Explanation:
When a body is moving, its motion is usually referenced to a frame of reference which could be stationary or moving also relative to another frame of reference. In this case you are frame of reference that is also moving relative to the earth or another stationary observer. The earth compared to other frames of reference on planet earth can be said to be a stationary frame of reference because its movement id not so obvious as much.
Basically when we say a body is moving at 5m/s we actually stating its velocity relative to the earth's frame of reference. In the case where a person is moving in the opposite direction to traveling car, the vector sum of their relative speeds is usually taken relative to another frame of reference usually the earth. When a car A and a car B are moving relative to each other in opposite directions, the speed of car A reliever to car B is always equal but opposite in direction to the speed of car B relative to the speed of car A. Mathematically both speeds will have opposite signs. That is Va/b = -Vb/a. (Read a relative to b and b relative to a.)
These speeds are usually greater than their actual speeds relative to a third frame of reference. Generally it is equal to the sum of their speeds relative to the third frame of reference (for example the earth). If I am walking at a speed of 1.5m/s relative to the earth and you were walking at a speed of 1m/s relative to the earth as well in the opposite direction. Then my speed relative to you would be equal to 2.5m/s and your speed relative to me would be -2.5m/s or the other way round (that is your speed relative to me is 2.5m/s and my speed relative to you is -2.5m/s). The value being positive or negative depends on the direction chosen as positive whether my direction or your direction.
Thank you for reading and I hope this was helpful to you.
