To find the recoil velocity of the rifle, we can use the principle of conservation of momentum. According to this principle, the total momentum before firing the shell is equal to the total momentum after firing the shell.
The momentum of an object is defined as the product of its mass and velocity. Let's denote the mass of the rifle as M and the initial velocity of the rifle as V. The shell has a mass of 50.0 grams, which is equal to 0.050 kg, and it leaves the rifle with a velocity of 400 m/s.
Now, let's set up the equation using the principle of conservation of momentum:
Total momentum before = Total momentum after
(M * V) + (m * u) = (M * V') + (m * v)
Where:
M = mass of the rifle (3.00 kg)
V = initial velocity of the rifle (to be determined)
m = mass of the shell (0.050 kg)
u = initial velocity of the shell (0 m/s since it is at rest before firing)
V' = final velocity of the rifle (to be determined)
v = final velocity of the shell (400 m/s)
Now, substitute the known values into the equation:
(3.00 kg * V) + (0.050 kg * 0 m/s) = (3.00 kg * V') + (0.050 kg * 400 m/s)
Simplifying the equation:
3.00 kg * V = 3.00 kg * V' + 20 kg * m/s
Since the mass of the shell is relatively small compared to the mass of the rifle, we can neglect its contribution to the overall momentum. Hence, the equation becomes:
3.00 kg * V = 3.00 kg * V'
Now we can solve for V', the final velocity of the rifle:
V' = V
Therefore, the recoil velocity of the rifle is equal in magnitude but opposite in direction to the initial velocity of the rifle. So, the recoil velocity of the rifle is 400 m/s (in the opposite direction).