We can use the conservation of energy to solve this problem.
We know the bullet goes in at 39m/s and leaves with 27m/s and some energy lost. We can model this using the kinetic equation energy.
The "U" is the energy lost when the bullet went through the bag. Solving for U, we get:
Next we know the bag is 48cm thick and that F*d=W, rearranging this equation we get:
F = 12.375N
We know the bullet goes in at 39m/s and leaves with 27m/s and some energy lost. We can model this using the kinetic equation energy.
The "U" is the energy lost when the bullet went through the bag. Solving for U, we get:
Next we know the bag is 48cm thick and that F*d=W, rearranging this equation we get:
F = 12.375N