Answer
The kinetic energy of sphere B is $~~5.5\times 10^{-9}~J$
Work Step by Step
We can use conservation of energy to find the kinetic energy of sphere B:
$K_2+U_2 = K_1+U_1$
$K_2 = 0+U_1-U_2$
$K_2 = (-\frac{G~M_A~M_B}{R_1})-(-\frac{G~M_A~M_B}{R_2})$
$K_2 = (\frac{G~M_A~M_B}{R_2})-(\frac{G~M_A~M_B}{R_1})$
$K_2 = \frac{(6.67\times 10^{-11}~N~m^2/kg^2)~(20~kg)~(10~kg)}{0.60~m}-\frac{(6.67\times 10^{-11}~N~m^2/kg^2)~(20~kg)~(10~kg)}{0.80~m}$
$K_2 = (2.22\times 10^{-8}~J)-(1.67\times 10^{-8}~J)$
$K_2 = 5.5\times 10^{-9}~J$
The kinetic energy of sphere B is $~~5.5\times 10^{-9}~J$
