A2L Item 066

Goal: Hone the vector nature of velocity.

Source: UMPERG-ctqpe142

A
child is standing at the rim of a rotating disk holding a rock. The
disk rotates without friction. The rock is thrown in the RADIAL
direction at the instant shown, which of the indicated paths most nearly
represents the path of the rock as seen from above the disk?

1. path (1)
2. path (2)
3. path (3)
4. path (4)
5. path (5)
6. cannot be determined

Commentary:

(4) is the correct path if the rock is thrown radially.

Background

Once thrown the components of the velocity of the rock lying in a
horizontal plane are constant so the rock will have a path which is a
straight line.

Questions to Reveal Student Reasoning

Identify a coordinate frame. What are the components of the velocity
vector immediately after the rock is thrown?

What is the radial component of the velocity if the rock follows path
(2)?

Is it possible to throw the rock in such a way that the rock follows
path (5)?

Suggestions

This item should be compared to 63.