• # question_answer Sand is being dropped on a conveyer belt at the rate of 2 kg per second. The force necessary to keep the belt moving with a constant speed of 3 $\text{m}{{\text{s}}^{\text{-1}}}$will be          [JEE ONLINE 19-05-2012] A) 12N B) 6N C) Zero D) 18N

 [b] Here, rate of fall of sand on conveyer belt,$\frac{dm}{dt}=2kg\,{{s}^{-1}}$ Conveyer belt speed $v=3\,m{{s}^{-1}}$ Force F = ? $F=v\frac{dm}{dt}=3\times 2=6N$