A person throws a ball up into the air, and the ball falls back toward Earth. At which point would the kinetic energy be the lowest?
1. at a point when the ball is still rising
2. when the ball leaves the person's hand
3. at a point before the ball hits the ground
4. when the ball is at its highest point
The correct answer is 1. at a point when the ball is still rising.
Kinetic energy is the energy of an object due to its motion. When the ball is still rising, its velocity is decreasing as it moves upward against the force of gravity. As a result, the kinetic energy of the ball is decreasing.
When the ball leaves the person's hand, it has initial kinetic energy given by its initial velocity.
At a point before the ball hits the ground, the ball is moving downward and its velocity is increasing due to acceleration from gravity. Therefore, the kinetic energy of the ball is increasing as it approaches the ground.
When the ball is at its highest point, its velocity is momentarily zero and therefore its kinetic energy is also momentarily zero. However, this is only a brief instant and not a sustained period of low kinetic energy.
The kinetic energy of an object is the energy it possesses due to its motion.
1. At a point when the ball is still rising: The kinetic energy of the ball is increasing as it gains speed while rising against the force of gravity. Therefore, the kinetic energy is not the lowest at this point.
2. When the ball leaves the person's hand: At this point, the ball has just started its motion, and its kinetic energy is relatively low compared to other points in its trajectory. So, the kinetic energy is generally lower when the ball leaves the person's hand.
3. At a point before the ball hits the ground: As the ball falls toward the ground, its speed increases, and so does its kinetic energy. Therefore, the kinetic energy is not the lowest at this point.
4. When the ball is at its highest point: At the highest point, the ball momentarily comes to a stop before reversing its motion and falling back down. Since the ball has zero speed at this point, its kinetic energy is also zero, making it the lowest point for kinetic energy.
Thus, the answer is 4. when the ball is at its highest point.
To determine at which point the kinetic energy is the lowest, we need to understand the concept of kinetic energy and how it relates to the motion of the ball. Kinetic energy is the energy an object possesses due to its motion. It depends on both the object's mass and its velocity.
In this scenario, the ball is thrown up into the air and then falls back to Earth. Let's analyze each option to find the point with the lowest kinetic energy:
1. At a point when the ball is still rising:
- Initially, as the ball is thrown up, its velocity increases while it rises.
- Since kinetic energy depends on velocity and velocity is still increasing at this point, the ball's kinetic energy is not the lowest here.
- Therefore, this is not the correct answer.
2. When the ball leaves the person's hand:
- Once the ball leaves the person's hand, it has an initial velocity determined by the force with which it was thrown.
- At this point, the ball has the highest kinetic energy since it has the highest velocity.
- Therefore, this is not the correct answer.
3. At a point before the ball hits the ground:
- As the ball falls towards the ground, its velocity increases due to the acceleration due to gravity.
- Since kinetic energy depends on velocity and the velocity is still increasing at this point, the ball's kinetic energy is not the lowest here.
- Therefore, this is not the correct answer.
4. When the ball is at its highest point:
- At the highest point of the ball's trajectory, its velocity becomes zero momentarily.
- Since kinetic energy depends on velocity, and the velocity is zero, the ball's kinetic energy is also zero at this point.
- This occurs because the ball has reached its maximum potential energy and is about to reverse its direction.
- Therefore, this is the correct answer. The kinetic energy is the lowest when the ball is at its highest point.
So, the correct answer is option 4: when the ball is at its highest point.