Since the bag was at rest, its initial momentum is zero. The velocity of the ball before collision is 500 ms-1.
<h3>Linear momentum</h3>
The term momentum in physics refers the product of mass and velocity. If we know mass of the object and its velocity, then we calculate the momentum.
Momentum before collision for the bullet = 0.01 kg × v
Momentum before collision for the bag = 0
Momentum after collision for the bag and bullet = (0.01 kg + 0.49 kg) 10 = 5 Kgms-1
The velocity of the bullet before collision = 0.01 kg × v + 0 = 5 Kgms-1
v = 5 Kgms-1/0.01 kg
v = 500 ms-1
Learn more about momentum: brainly.com/question/904448
Our data are,
State 1:

State 2:

We know as well that 
To find the mass we apply the ideal gas formula, which is given by

Re-arrange for m,

Because of the pressure, temperature and volume ratio of state 1 and 2, we have to

Replacing,

For conservative energy we have, (Cv = 0.718)

Hmm, I will come back to this one just to help. :)