Answer :
W=K_B-K_A
W=m_B v^2/2-m_A v^2/2=(m_B-m_A)v^2/2
W=(2000-1200) 〖40〗^2/2=640000 J=640 kJ.
W=m_B v^2/2-m_A v^2/2=(m_B-m_A)v^2/2
W=(2000-1200) 〖40〗^2/2=640000 J=640 kJ.