The Total solution for NCERT class 6-12
Given,radius of wheel, r = 35 cmCircumference of the wheel = 2╧Аr= 2 x┬а(22/7)┬аx35 = 220 cmBut speed of the wheel = 66 kmh-1=┬а(66x1000/60)┬аm/mm= 1100 x 100 cm min-1= 110000 cm min-1тИ┤ Numberof revolutions in 1 min=┬а(110000/220)=500 revolutionHence, required number of revolutions per minute is 500.