在输入roslaunch mbot_gazebo view_mbot_gazebo_empty_world.launch时，就会出现这种情况

RLException: [view_mbot_gazebo_empty_world.launch] is neither a launch file in package [mbot_gazebo] nor is [mbot_gazebo] a launch file name
The traceback for the exception was written to the log file

能告诉我怎么怎么解决吗！！卡在这里卡了好久了，最好详细一点