Exercise 18.1
Four rows, and in each one a different box is empty. Only the second row hides a trap, and it is a trap about units rather than about work.
The task
Copy this table into your exercise book and complete it. Every row uses the same relationship between the three columns.
| Force | Distance the force acts through | Work done |
|---|---|---|
| 20 N | 2 m | ............. |
| .......... | 80 cm | 24 J |
| 15 N | .......... | 22.5 J |
| 0.75 N | 8 m | ............. |
How to approach each row
The same formula answers all four; which box is empty decides whether you multiply or divide.
- Row 1 and row 4 give you the force and the distance, so multiply them.
- Row 2 gives the work and the distance, so divide the work by the distance to find the force.
- Row 3 gives the work and the force, so divide the work by the force to find the distance.
80 cm is not 80 m
The second row gives the distance in centimetres while every other row is in metres. Convert it to 0.8 m before dividing, or the force you find will be a hundred times too small.