Answer:
C) 1200 rpm
Explanation:
[tex]D_1[/tex] = Diameter of bigger pulley = 24 inch
[tex]D_2[/tex] = Diameter of smaller pulley = 8 inch
[tex]N_1[/tex] = Speed of bigger pulley = 400 rpm
[tex]N_2[/tex] = Speed of smaller pulley
The relation between revolutions per minute and diameter is that they are inversely proportional.
[tex]\frac{N_1}{N_2}=\frac{D_2}{D_1}\\\Rightarrow \frac{400}{N_2}=\frac{8}{24}\\\Rightarrow N_2=\frac{24\times 400}{8}\\\Rightarrow N_2=1200\ rpm[/tex]
The number of revolutions per minute of the smaller pulley is 1200 rpm