When making a sound source near a reflective surface, such as making a person at a podium, the sound can reflect off of the surface an create phase interference known as comb filtering. An approach to solve this problem is...

1. By removing the reflector or reflecting elements

2. By using absorbing material on the reflecting surfaces.

Explanation:

To solve problems caused by reflecting surfaces, you can remove the reflector or reflecting elements. However, sometimes it is enough to turn/move the reflecting element and change the reflections. Furthermore, using absorbing material on the reflecting surface can help reduce comb filtering as well.

In some cases, it is possible to place the sound source so close to the reflecting surface, that there is no suspension between the direct sound and the reflected sound.

b. lifting dumbbell weight at 20-degree angle from the body after a 45-degree angle

ingenuity says that the answer is 2.7 m.