Question

Shown below is a belt–pulley arrangement. How many pulleys are rotating clockwise?

Hint:

Decide the belt direction on each contacted side of a pulley. A quick mnemonic: right side going \(\uparrow\) \(⇒\) CCW, right side going \(\downarrow\) \(⇒\) CW; left side is the opposite.

Answer 1

Step 1: Fix belt motion and the first pulley.
The figure marks the belt moving upward on the two right-hand vertical runs, and the curved arrow on the nearby pulley shows its sense. Treat that pulley as clockwise.
[2pt] Step 2: Propagate directions along the belt.
For a taut belt without slip, the pulley rotates so that the belt-point velocity at the contact side matches the belt direction.
\(⇒\) When the belt rises on a pulley’s right side, that pulley must be counterclockwise; when it rises on the left side, it must be clockwise (and similarly for falling runs).
Now trace the belt from the reference pulley to each next pulley in order; the sense alternates according to which side is contacted. Counting this through the entire serpentine path yields five pulleys with clockwise rotation.