Pressure between the inside chest wall and the outside of the lungs normally remains negative. Explain how pressure inside the lungs can become positive (to cause exhalation) without muscle action.

by doing rapid shallow breathing and pursed lip breathing  

Explanation:

Pressure with in the chest wall and the outside of the lungs remains negative because the intrapleural pressure is always lesser than the intra-alveolar pressure or atmospheric pressure. In general forced expiration leads to an increasing positive pressure in pleura. This happens because the pleura airway gets compressed and the size of airway reduces thereby forcing expiration.  

People who are able to resist airway can increase airflow by doing rapid shallow breathing and pursed lip breathing  

total distance travelled = 60 miles

total time taken =1.5 hours

average speed = total distance / total time

60 / 1.5

= 40

therefore, average speed = 40 m/h

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the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

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im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.