$\left|\overrightarrow{\mathrm{a}}_{\mathrm{BA}}\right|=4 \mathrm{~m} / \mathrm{s}$
$\text { Apply }\left(\mathrm{v}^2=\mathrm{u}^2+2 \mathrm{as}\right)_{\text {relitive }}$
$\mathrm{O}=(40)^2+2(-4)(\mathrm{S})$
$\mathrm{S}=200 \mathrm{~m}$
Remaining distance$=300-200=100 \mathrm{~m}$