function main(){
  //Master Sheet
  var sprsheet = SpreadsheetApp.getActiveSpreadsheet();
  var master_sheet = sprsheet.getSheetByName("ENTRATE MAIN");
  var master_range = master_sheet.getRange("AJ2:J50");
  //Second Sheet
  var sheetName = master_sheet.getRange("Z1").getValue();
  var second_sheet = sprsheet.getSheetByName(sheetName);
  var lastrow = second_sheet.getLastRow();

  var master_data = master_range.getValues();

  if (lastrow > 50){ //This is in case your second sheet has less than 50 rows before copying the data
    //We have to check the previous 49 rows in case the data is already there
    var second_range = second_sheet.getRange("AJ"+(lastrow-49)+":J"+(lastrow));
    var second_data = second_range.getValues();

    if (!isCopied(master_data, second_data)){
      //Data is not there so we copy it in the next 49 rows
      second_range = second_sheet.getRange("AJ"+(lastrow+1)+":J"+(lastrow+49));
      second_range.setValues(master_data);

    }
  } else {
    //The second sheet has less than 50 rows so the data is obviously not there
    var second_range = second_sheet.getRange("AJ"+(lastrow+1)+":J"+(lastrow+49));
    second_range.setValues(master_data);

  }
}

function isCopied(master_data, second_data){
  for (i in master_data){
    for (j in master_data[i]){
      if (master_data[i][j] != second_data[i][j]){
        return false;
      }
    }

  }
  return true;
}