The concept of relative motion is applied when we want to analyze the motion of an object with respect to a different frame of reference. It is used to describe the motion of an object relative to another object or observer, taking into account their respective velocities.
Relative motion can be applied in various scenarios, such as:
Observing the motion of objects from a moving vehicle or platform: When you are moving in a car, for example, and you observe objects outside the car, their apparent motion will depend on both their actual motion and the motion of the car. Relative motion helps in understanding how the objects appear to move relative to your frame of reference inside the car.
Analyzing motion in different reference frames: Relative motion allows us to analyze the motion of an object from different perspectives. For example, if two objects are moving relative to each other, we can choose one of them as the reference frame and describe the motion of the other object with respect to it.
Regarding your specific question, if a body is thrown upward with acceleration, you can certainly apply the concept of relative motion to find the effective acceleration. However, it's important to note that acceleration is a measure of how an object's velocity changes over time. When an object is thrown upward, its initial acceleration is determined by the force applied to it, such as the force exerted by your hand. Once the object is released, the only force acting on it is the force of gravity pulling it downward.
If you want to find the effective acceleration of the body as it moves upward, you would need to consider the acceleration due to gravity acting in the opposite direction. The net acceleration would be the difference between the initial upward acceleration and the acceleration due to gravity. However, it's worth mentioning that as the object moves upward, the acceleration due to gravity gradually reduces its upward speed until it reaches its highest point and starts to descend.
In summary, while relative motion can be applied to analyze the motion of an object thrown upward, it is important to consider the forces acting on the object, such as the initial acceleration and the acceleration due to gravity, to determine the effective acceleration at any given point during its motion.