The surface is frictionless, so there is no frictional force acting on the ball. There are no other forces acting on the ball in the horizontal direction, so it's a uniform motion with constant speed. Therefore, the velocity of the ball will remain the same for the entire duration of the motion, and so after 5 seconds the velocity is still 15 m/s.
Answer:
When the volume increases or when the temperature decreases
Explanation:
The ideal gas equation states that:

where
p is the gas pressure
V is the volume
n is the number of moles of gas
R is the gas constant
T is the gas temperature
Assuming that we have a fixed amount of gas, so n is constant, we can rewrite the equation as

which means the following:
- Pressure is inversely proportional to the volume: this means that the pressure decreases when the volume increases
- Pressure is directly proportional to the temperature: this means that the pressure decreases when the temperature decreases