Many cultures around the world still use a simple weapon called a blowgun, a tube with a dart that fits tightly inside. A sharp breath into the end of the tube launches the dart. When exhaling forcefully, a healthy person can supply air at a gauge pressure of 6.0 kPa. Required:
What force does this pressure exert on a dart in a 1.5-cm-diameter tube?

F = 1.06N

Explanation:

In order to calculate the force that produces the given pressure you take into account the following formula:  

         (1)

P: pressure = 6.0kPa = 6.0*10³ Pa

F: force = ?

A: cross-sectional area of the tube = π r^2

r: radius of the tube = 1.5cm/2 = 0.75cm = 0.75*10^-2 m

You solve the equation (1) for F, and replace the values for the area A and the pressure P:

The force tha produces a pressure of 6.0kPa in a tube with a diameters of 1.5cm is 1.06N

the moving of the box is a result of centripetal force. think of that  as a car or a truck in this case creates a turn, the force of friction performing upon the turned wheels of the car runs centripetal force obligatory for circular motion for the things inside it.