A safety team is setting emergency-stop requirements for a driver-operated railway inspection vehicle. The test data are shown in the table.
| Quantity | Value |
|---|---|
| mass of vehicle | 6000 kg |
| speed when the warning signal appears | 36 km/h |
| driver's reaction time | 0.70 s |
| braking distance, measured from when the brakes act until the vehicle stops | 25 m |
| speed conversion | 1 m/s=3.6 km/h1\ \mathrm{m/s}=3.6\ \mathrm{km/h}1 m/s=3.6 km/h |
The track ahead must be clear for at least the stopping distance. What are the minimum clear length of track and the magnitude of the mean resultant braking force?
25 m25\ \mathrm{m}25 m and 24 000 N24\,000\ \mathrm{N}24000 N
32 m32\ \mathrm{m}32 m and 24 000 N24\,000\ \mathrm{N}24000 N
25 m25\ \mathrm{m}25 m and 12 000 N12\,000\ \mathrm{N}12000 N
32 m32\ \mathrm{m}32 m and 12 000 N12\,000\ \mathrm{N}12000 N