Answer:
m = 33833.3 kg
Explanation:
let M be the mass of boxcar 1 and V be the velocity of boxcar 1, let m be the mass of boxcar 2 and v be the velocity of boxcar 2.
from conservation of linear momentum:
M×Vi + m×vi = vf(M + m)
M×Vi - M×vf = m×vf - m×vi
  M(Vi - vf) = m(vf - vi)
        m = [M(Vi - vf)]/(vf - vi)
          = [(8700)(11.0 - 4.00)]/(4.00 - 2.2)
          = 33833.3 kg
Therefore, the mass of boxcar 2 is 33833.3 .
