The key projectile motion is that gravity allows downward only
The initial volume of the gas is

while its final volume is

so its variation of volume is

The pressure is constant, and it is

Therefore the work done by the gas is

where the negative sign means the work is done by the surrounding on the gas.
The heat energy given to the gas is

And the change in internal energy of the gas can be found by using the first law of thermodynamics:

where the positive sign means the internal energy of the gas has increased.
Answer:
The terminal speed of this object is 12.6 m/s
Explanation:
It is given that,
Mass of the object, m = 80 kg
The magnitude of drag force is,

The terminal speed of an object is attained when the gravitational force is balanced by the gravitational force.



On solving the above quadratic equation, we get two values of v as :
v = 12.58 m/s
v = -15.58 m/s (not possible)
So, the terminal speed of this object is 12.6 m/s. Hence, this is the required solution.
72s for 24 complete oscillations.
Thus, a complete oscillation takes 72/24=3s
Answer: period T=3s