(II) Determine the fraction of kinetic energy lost by a neutron $\left(m_{1}=1.01 \mathrm{u}\right)$ when it collides head-on and elastically with a target particle at rest which is $(a)$ i $\mathbf{H}(m=1.01 \mathrm{u}) ;$ (b) $^{2} \mathrm{H}$ (heavy hydrogen, $m=2.01 \mathrm{u} ) ;(c) \frac{12}{6} \mathrm{C}(m=12.00 \mathrm{u}) ;$ (d) $\frac{208 \mathrm{Pb}}{82 \mathrm{Pb}}($ lead $, m=208 \mathrm{u})$