One end of a horizontal string of linear density 4.8*10^-4kg

One end of a horizontal string of linear density 4.8*10^-4kg/m is attached to a small amplitude mechanical 60-Hz vibrator.The string passes over a pulley,a distance L=1.40m away,and weights are hung from this end.What mass must be hung from this end of the string to produce (a)one loop?,(b)two loops?And in this problem,the length of the string may be adjusted by moving the pulley.If the hanging massis fixed at 0.080kg,how many different standing wave patterns may be achieved by varying L between 10cm and 150cm?首先求解释,好的追分,万分感激~%>_