Question

When you throw a ball upward, its kinetic energy ____ (DECREASES,INCREASES,REMAINS THE SAME) and its potential energy _____ (DECREASE,INCREASES, REMAINS THE SAME) . When the ball reaches maximum height, its kinetic energy is at a ____ (maximum, minimum).

Answer 1

When you throw a ball upward, its kinetic energy decreases and its potential energy increases. When the ball reaches maximum height, its kinetic energy is at a minimum.

Explanation:

- When the ball is thrown upward, its kinetic energy decreases. In fact, the kinetic energy of the ball is given by

$K=\frac{1}{2}mv^2$

where m is the mass of the ball and v its speed. We see that the kinetic energy is directly proportional to the speed: since the speed of the ball decreases as the ball gets higher, its kinetic energy decreases as well.

- the potential energy increases. In fact, the potential energy of the ball is given by

$U=mgh$

where g is the gravitational acceleration and h is the height above the ground. We see that U is directly proportional to h, therefore as the ball gets higher, h increases and the potential energy increases as well.

- When the ball reaches maximum height, its kinetic energy is minimum. To be more precise, the kinetic energy becomes zero. In fact, at the point of maximum height the speed of the ball becomes zero (because the ball changes direction, it starts going downward), so v=0 in the formula of the kinetic energy and therefore the kinetic energy is zero.

Answer 2

When the ball goes upward, the velocity is decreasing. Therefore, the kinetic energy is decreased. The potential energy when the ball's height increases also increases. When the ball reaches maximum, the velocity becomes zero and the kinetic energy is minimum.