Chapter 6.1, Problem 8SSC

To determine

To Draw: The free-body and motion diagrams of the ice cube at two points on the table and two points in air

Explanation of Solution

Introduction:

A free-body diagram shows the total forces acting on a body whereas the motion diagram is an illustration of the velocity of the body.

Free body diagram of the ice cube anywhere on the table:

The ice cube slides on the table with constant velocity. So the net force acting on it is zero in the horizontal direction. When it is anywhere on the table the force acting on it are the normal force ${\text{F}}_{\text{N}}$ (normal to the table and in Upward direction) and the gravitational force ${\text{F}}_{\text{g}}$ in the down ward direction. These two forces are equal and opposite as the cube has no vertical velocity change.

Thus the net force in the vertical direction on the ice cube is also zero.

Free body diagram anywhere in air:

When the ice cube is in air the only force acting is the gravitational force in the down ward direction.

Motion Diagram when the ice cube on the table:

On the table the acceleration is zero, hence it moves with the same constant velocity.

Motion diagram when the ice cube in air:

In air the cube has an acceleration in the downward direction. Hence the vertical component of

velocity goes on increasing as it goes down, whereas the horizontal component of velocity remains unchanged.

Free body diagram of the ice cube anywhere on the table.

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Free body diagram anywere in air

Motion Diagram when the ice cube on the table

Motion diagram when the ice cube in air