$(document).ready(function () {
    showHiddenDiv();
    $("input[@name='ctl00$mainContent$mobileAlerts$rbMobileAlerts']").click(showHiddenDiv);
    
    
});

function showHiddenDiv()
{
    if ($("input[@name='ctl00$mainContent$mobileAlerts$rbMobileAlerts']:checked").val() == "Yes")
        $('.mobileForm').show();
    else
        $('.mobileForm').hide();   
}