Correct Answer - Option 1 : 0.25
Explanation
The effect of contaminant films such as water, organic detritus, or grease from vehicular traffic, all of which form barriers to contact and thereby reduce the coefficient of friction. Surface contaminants combined with the smooth rail surface mean that, compared with cars and lorries, railway vehicles must operate with quite low levels of grip.
The coefficient of friction between the wheels and rail is at most 0.5 on a dry rail and 0.3 on a wet one, and less in frost. To be on the safe side, it is usual to assume a value of 0.2 in daily operation.
∴ The most appropriate answer is 0.25