Because hyperventilation clears out more of the carbon dioxide out of your system, and it's the build-up of CO that controls your breathing reflex. Do note that hyperventilating is a Bad Idea, particularly when diving. Lack of oxygen is what knocks you unconscious, but it's the build up of CO which forces you to breathe.
because you just can
So they can hold their breath longer. By hyperventilating they remove excess CO2 in their body, then when they take a deep breath, they are able to have more oxygen in their body, thus being able to hold their breath longer. It can be dangerous because breathing is regulated by the level of CO2 in our body, and when too much is removed, the body doesn't know when breathe again. http://www.deep-six.com/page73.htm
make you able to hold for breath for longer than 7 seconds
No, generally speaking they would not because adults and older kids have bigger more developed lungs. One factor that might make younger kids be able to hold their breath longer is if and older person is a smoker.
Yes you would because the sand would suck you in until you can no longer reach the surface. Therefore you wouldn't be able to breath
Not being able to take a deep breath is not always considered shortness of breath. If you are exerting yourself, where you need more air but can't take a deep breath, you would have a shortness of breath.
Yes.
No. You should be able to live a normal life if you take the medicine.
A normal adult human being can hold their breath for around 1:30 to around 2:00 and some adults may be able to last longer. :)
You would not be able too.
a good lung capacity has to have room and a large chest cavity
Depending on your current physical condition you may only be able to run slowly and for only short distances before running out of breath. Some people start a running program using a walk-run strategy where you run a short distance then walk to recover. As you continue training, and your fitness level increases you will be able to run for longer distances and your recovery walks will shorten. Eventually you will be able to run without running out of breath.