Free-body Diagrams

Draw free-body diagrams which indicate all the forces, and the direction of these forces, that act on the bodies indicated in the following. Don't ignore friction or air resistance unless told to. We've underlined the body (or bodies) for which you are to draw the diagram.

1. A mass hanging from a string.

2. A mass sliding down a frictionless inclined plane.

3. A baseball being hit by a bat.

4. A baseball flying through the air after being hit by a bat.

5. A car moving down the road at constant speed in a straight line.

6. The moon in its orbit.

7. A car driving on a level, circular track.

8. A car is pushing a truck. Draw free body diagrams for both the car and the truck.

9. A block being pulled across the table by a string which is attached to the block.

10. A ladder against a wall, with a man standing on the ladder.

11. A diving board with a woman standing at the end of it.

In the example of the book on a table, the two forces (support and gravity) were equal and opposite. Are they action-reaction pairs as in Newton's third law? This is tricky, but important, so think about it. For instance, are the support force and gravity always equal in magnitude? Explain your thinking.

One last problem:

Two blocks are connected by a string, and a second string attached to the right-most block is pulled to the right with a force of 50 N. What is the acceleration of this system? [Hint: treat the two blocks as a single body] There is no friction.

What is the tension in the string joining the two blocks? [Hint: Draw a free body diagram for the 4 kg block.]