Answer
The mass of the canister is 81.8 kg.
Work Step by Step
We can use conservation of momentum to solve this question.
$m_c~v_{c1} + m_a~v_{a1}= m_c~v_{c2} + m_a~v_{a2}$
$m_c~v_{c1} + 0 - m_c~v_{c2} = m_a~v_{a2}$
$m_c = \frac{m_a~v_{a2}}{v_{c1} - v_{c2}}$
$m_c = \frac{(78.4~kg)(2.40~m/s)}{3.50~m/s - 1.20~m/s}$
$m_c = 81.8~kg$
The mass of the canister is 81.8 kg.
