search for a form field with jquery

I have a select field in html, it is hidden along with a div and disabled.

From the selection of a value (select), it should appear on the screen and be enabled.

I am not able to make the select field enable, it always appears disabled.

 $('#'+div).find(':select').prop('disabled', false);

I'm using the above code to search for the select within a div and then the disabled to false. I know that: select is not supported. I would like to know how to look for a select type field of a div.

HTML and JS Codes:

HTML:

<div class="form-group">
   <label class="col-sm-2 control-label">Finalidade</label>
     <div class="col-sm-6" id="ocultar">
        <select name="finalidade" class="chosen-select input-md form-control" required>
          <option value="" selected>Selecione uma Finalidade</option>

        </select>
     </div>
</div>
<div id="ocultar_div" style="display: none;">
    <fieldset>
       <div class="form-group">
          <label class="col-sm-2 control-label">Colaborador</label>
             <div class="col-sm-6">
                 <select name="colaborador" class="chosen-select input-md form-control" required disabled>
                     <option value="0" selected>Selecione um Colaborador</option>

                 </select>
             </div>
     </div>
  </fieldset>

JS:

$("select[name=finalidade]").change(function(){
       var tipo = $(this).val();
       var iddiv = $("select[name=finalidade]").parent().attr('id') + '_div'; 
       MostrarEsconderDiv(tipo,iddiv);
    });

function MostrarEsconderDiv(tipo, div) {
    var elemento = $("#"+div).find("select");
    if (tipo == 3) {      
      $("#"+div).css("display", "block");
      elemento.prop("disabled", false);
    } else {
      $("#"+div).css("display", "none");
      elemento.prop("disabled", true);
    }

}