which of the following statements is/are correct and why?(a)the coeficient of static friction may be equal to the coeficient of kinetic friction(b)the value of coeficient of friction, s can'be greater than one(c)the value of friction is always costant under moderate conditions(d)if the surface is rough,the value of static friction can't be zero

dear sanket sit

all answer r correct

Occasionally it is maintained that µ is always < 1, but this is not true.a tire on concrete may have a coefficient of friction of 1.7.

The coefficient of friction is an empirical measurement – it has to be measured experimentally, and cannot be found through calculations. Rougher surfaces tend to have higher effective values. Most dry materials in combination have friction coefficient values between 0.3 and 0.6. Values outside this range are rarer, but teflon, for example, can have a coefficient as low as 0.04

The coefficient of kinetic friction is  usually less than the coefficient of static friction for the same materials. In fact, Richard Feynman reports that "with dry metals it is very hard to show any difference." Finally, new models are beginning to show how kinetic friction can be greater than static friction.

Regards

Badiuddin