The answer i think would be D
Answer:
The pressure must have increased in the process
Explanation:
The State Equation for gasses reads: 
where P is the gas' pressure, V its volume, n the number of moles of gas, R the gas constant and T the temperature in degrees Kelvin.
If the temperature of the gas doesn't change in the described process, the right hand side of the equation stays the same. If that is the case, given that when the Volume of the gas diminishes from 75 liters to 50 liters, then the pressure must have increased to keep that product "P * V" constant:

So the pressure must have gone up to 450 kilopascals.
Answer:
The common velocity v after collision is 2.8m/s²
Explanation:
look at the attachment above ☝️
The spring has a spring constant of 1.00 * 10^3 N/m and the mass has been displaced 20.0 cm then the restoring force is 20000 N/m.
Explanation:
When a spring is stretched or compressed its length changes by an amount x from its equilibrium length then the restoring force is exerted.
spring constant is k = 1.00 * 10^3 N/m
mass is x = 20.0 cm
According to Hooke's law, To find restoring force,
F = - kx
= - 1.00 *10 ^3 * 20.0
F = 20000 N/m
Thus, the spring has a spring constant of 1.00 * 10^3 N/m and the mass has been displaced 20.0 cm then the restoring force is 20000 N/m.