Question

The image shows a pendulum that is released from rest at point A. Shari tells her friend that no energy transformation occurs as the pendulum swings between point B and point D.



What is the best response that Shari’s friend could make?

She could agree with Shari because the pendulum is at the same height and would have the same gravitational potential energy at both positions.

She could agree with Shari because the pendulum has the same amount of mechanical energy throughout its swing.

She could disagree with Shari because the pendulum converts kinetic energy into gravitational potential energy, then back into kinetic energy.

She could disagree with Shari because the pendulum converts gravitational potential energy into kinetic energy, then back into gravitational potential energy.

Answer 1

is  D    the  right  answer

Answer 2

Answer:

She could disagree with Shari because the pendulum converts gravitational potential energy into kinetic energy, then back into gravitational potential energy.

Explanation:

The energy of the pendulum is constantly converted from gravitational potential to kinetic, and back.

In fact:

- the gravitational potential energy of the pendulum is given by:

$U=mgh$

where m is the mass of the pendulum, g is the gravitational acceleration, and h is the height of the pendulum above the ground

- The kinetic energy of the pendulum is given by:

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

where v is the speed of the pendulum.

Therefore, when it is at a higher position, the pendulum has a greater potential energy, while when it is at a lower position, the pendulum has a greater kinetic energy (because its speed is higher).

In this example:

- when the pendulum swings from B to C, part of its gravitational potential energy is converted into kinetic energy (because the height decreases but the speed increases), and when the pendulum goes from C to D, the kinetic energy is converted back into gravitational potential energy (because the height increases and the speed decreases)