## Essential University Physics: Volume 1 (3rd Edition)

$v=1.08 \ Mm/s$ $m_2=4 \ u$
We know the following equation for elastic collisions: $v_{1f}=\frac{m_1-m_2}{m_1+m_2}v_{1i}+\frac{2m_2}{m_1+m_2}v_{2i}$ $-8.62=\frac{1-m_2}{1+m_2}(6.9)+\frac{2m_2}{1+m_2}(-2.8)$ $m_2=4 \ u$ We use conservation of momentum to find: $1(6.9)+4(-2.8)=1(-8.62)+4(v)\\ v=1.08 \ Mm/s$