A doorknob has a knob radius of 3 centimetres and a spindle radius of 1 centimetre. How much easier is it to turn the spindle using the knob compared to gripping the spindle directly?

Correct answer to question 171 (Mechanical Comprehension): about 3 times easier

Method

The mechanical advantage is knob radius divided by spindle radius: 3 / 1 = 3, making it three times easier to apply enough torque.