A2L Item 066
- Description: Indicate the path of a rock thrown radially from a rotating platform.
- Goal: Hone the vector nature of velocity.
- Source: UMPERG-ctqpe142
- Keywords: Mechanics, Rotational Motion, Vectors, Velocity
The question for students:
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?
- path (1)
- path (2)
- path (3)
- path (4)
- path (5)
- cannot be determined
Commentary for teachers:
Answer
(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.