An archive uses a drive unit to move a shelf at constant speed. The drive unit must exert a constant force of 120 N in the direction of motion while the shelf moves 6.0 m in 9.0 s.
Four drive units are available.
| Drive unit | Useful power output |
|---|---|
| P | 0.67 W |
| Q | 20 W |
| R | 80 W |
| S | 180 W |
Which drive unit has the smallest useful power output that is sufficient to move the shelf as required?
drive unit P
drive unit Q
drive unit R
drive unit S