Introduction

The permissible speed on a crossing can be calculated based on the crossing number N. There are four options provided: (a) 1.2 N, (b) 2.4 N, (c) 3.6 N, and (d) 4.8 N. In this explanation, we will determine the correct option and provide a detailed explanation.

Calculation Method

To calculate the permissible speed on a crossing, we need to consider the crossing number N. Let's evaluate each option to determine which formula is correct.

Option (a) 1.2 N

If the permissible speed is given by 1.2 N, it means that the speed is directly proportional to the crossing number. This option implies that as the crossing number increases, the permissible speed also increases. However, there is no explanation provided for this relationship.

Option (b) 2.4 N

If the permissible speed is given by 2.4 N, it means that the speed is directly proportional to the crossing number. This option also implies that as the crossing number increases, the permissible speed also increases. However, there is no explanation provided for this relationship.

Option (c) 3.6 N

If the permissible speed is given by 3.6 N, it means that the speed is directly proportional to the crossing number. This option also implies that as the crossing number increases, the permissible speed also increases. However, there is no explanation provided for this relationship.

Option (d) 4.8 N

If the permissible speed is given by 4.8 N, it means that the speed is directly proportional to the crossing number. This option also implies that as the crossing number increases, the permissible speed also increases. However, there is no explanation provided for this relationship.

Conclusion

Based on the given options, it is clear that all four options suggest a direct proportionality between the crossing number N and the permissible speed. However, without additional information or explanation, it is not possible to determine the correct formula to calculate the permissible speed on a crossing. Therefore, the correct option cannot be determined.

D