Ideal Pulley

T_{1} = T_{2} = T \sum F = 0 on the pulley

A frictionless pulley changes the direction of a cable but not the tension. Each ideal rope segment has the same T. Count how many supporting strands to lift a load (mechanical advantage).

$T$ (N): Cable tension
$W$ (N): Suspended load

Step-by-step solved example

A block hangs from two ideal vertical strands (movable pulley). What pull P lifts W = 800 N at constant speed?

Ideal pulley: tension is constant; count supporting strands for MA.

1. Strands
Two strands share W, so 2T = 800 N.
2. Pull
P = T = 400 N.
$P = 400 t e x t N$

Answer: P = 400 N

10 practice questions

0/10 correct

1.Ideal pulley friction is

2.Fixed pulley (one strand down to W) gives P =

3.Four supporting strands, slow lift. P =

4.A non-ideal pulley with friction has

5.Belt around a capstan uses

6.If P lifts W at constant speed, net acceleration is

7.Movable pulley attached to W with both strands up: T =

8.Cable weight is often neglected on the FE unless

9.Direction change of 180° on an ideal pulley

10.The pin of a fixed ideal pulley carrying two vertical strands of T supports