Question

We stick a inextensible adhesive tape on a tabletop. We grab one end of it and pull it back horizontally and uniformly with a velocity of 4 cm/s. What is the velocity (in cm/s) of the middle of the moving part of the tape?

Answer 1

4

Answer 2

The tape is inextensible, and the "moving part" refers to a segment of constant length. The pulled end moves at 4 cm/s. Due to inextensibility and constant length of the moving part, the peeling point (where the tape leaves the table) must also move at 4 cm/s. Since both ends of the moving part move at the same velocity, the entire moving part translates as a rigid body. Thus, every point on this moving part, including its middle, moves at 4 cm/s.