Answer
With $M=20 \mathrm{kg}$ and $m=10 \mathrm{kg}$ , energy conservation leads to
$$
K_{i}+U_{i}=K+U \Rightarrow 0+0=K-2 \frac{G m M}{r}
$$
which yields $$K=2 G m M / r=5.3 \times 10^{-8} \mathrm{J}$$
Work Step by Step
With $M=20 \mathrm{kg}$ and $m=10 \mathrm{kg}$ , energy conservation leads to
$$
K_{i}+U_{i}=K+U \Rightarrow 0+0=K-2 \frac{G m M}{r}
$$
which yields $$K=2 G m M / r=5.3 \times 10^{-8} \mathrm{J}$$
