#m_a:90 kg" mass of astronaut "#
#m_o:7 kg" mass of object"#
#"let total momentum before thrown the object be "Sigma P_b#
#v_a:0" speed of astronaut"#
#v_o:0" speed of object"#
#Sigma P_b=m_a*v_a +m_o*v_0#
#v_a=0" , "v_o=0#
#Sigma P_b=90*0+7*0=0#
#"let total momentum after thrown the object be "Sigma P_a#
#u_a:?"speed of astronaut after thrown the object"#
#u_o:2/9 m/s" speed of object thrown."#
#Sigma P_a=m_a*u_a+m_o*u_o#
#Sigma P_a=90*u_a+7*2/9#
#Sigma P_a=90*u_a+14/9#
#"According to the principle of momentum conservation, the total"# #"momentum before the object is thrown is equal to the total"# #"momentum after the object is thrown."#
#Sigma P_b=Sigma P_a#
#0=90*u_a+14/9#
#90*u_a=-14/9#
#u_a=-14/(90*9)#
#u_a=-14/810#
#u_a=-0.02 m/s" rounded the two decimal place."#
#"Minus sign tells us that the direction of the speed of astronaut "#
#"is opposite to the direction of the speed of object."#