Problem Diagram

Jim Knowitall just started a new job washing windows. He decides to spread the two ropes further apart at the top so the platform will be more stable (or so he thinks).

What is known:

• A wind gust causes the platform to swing.
• The ropes rotate at a constant angular velocity of 10°/s counterclockwise.
• The current vertical distance is 20 feet.
• The ropes are 30° off the vertical.
• The platform is initially horizontal and is 6 feet wide.

What is the angular velocity of the platform when the ropes are spread at 30° to the vertical? Is it safe?

• One approach is to use the relative velocity equation, as was done in the previous section.
• A second, and sometimes easier approach is to use the concept of "Instantaneous Center of Zero Velocity" (IC).
• To use the IC method, the velocities of any two points on the body are needed.