Question 16
A cyclist pushes straight down on a bicycle pedal at the instant the pedal is at its highest point. What is the moment about the pedal axle?
The right answer is the one marked above.
There is no moment, because the perpendicular distance is zero. With the pedal at the top, the line of action of a downward push runs straight through the axle.
It is wrong to reason that the moment must be largest because the pedal is far from the axle. What is measured is not the distance to the pedal but the perpendicular distance to the line of action.