The diameter of the driving wheel of a bus is 140cm. How many revolutions per minute must the wheel make in order to keep a speed of 66 kmph?

• 250 rpm
  
  Let number of revolutions (in rev per min) needed be n
  n rev per min = 60*n rev per hour
  
  1 revolution = 2*pi*r = pi * diameter = pi * 140 cm
  = pi * 140 / 100000 km
  
  60 * n rev per hour = 60*n*pi*140/100000 km per hour ( = 66, given)
  n = (66 * 100000) / (60 * 140 * pi)
  = 250 rev per min
• 13 years agoHelpfull: Yes(3) No(0)
• 250 revolutions per Minute
  
  1 revolution = circumference of wheel = π d
  = 3.14 × 140 = 439.6 cm
  66 km = 66000 meters = 6600000 cm
  revolutions in 66 km = 6600000/439.6 = 15013.6 per hr.
  = 15013.6/60 = 250.22 ≈ 250 revolutions per minute
  
• 13 years agoHelpfull: Yes(3) No(2)