Which of the following statement(s) is/are incorrect regarding coefficient of friction? (i) It decreases for smooth pavement (ii) It decreases for wet pavement (iii) It decreases with increase in temperature (iv) It increases with increase in tyre pressure
- A(i) and (ii)
- B(ii) and (iii)
- COnly (iii)
- D(iii) and (iv)Correct
Solution
Concept
Factors affecting pavement skid resistance and coefficient of friction
Formula
NONE
Step-by-step solution
1. Statement (i) is correct: Smooth pavements offer lower macro-texture and lower friction. 2. Statement (ii) is correct: Water acts as a lubricant, reducing friction on wet pavements. 3. Statement (iii) is incorrect: Friction varies with rubber viscoelasticity and does not strictly decrease with temperature. 4. Statement (iv) is incorrect: Higher tyre pressure decreases contact area, reducing the coefficient of friction rather than increasing it. 5. Therefore, the incorrect statements are (iii) and (iv). Answer: D
Explanation
The question asks for INCORRECT statements. Friction decreases on smooth pavements (i is true) and wet surfaces (ii is true). An increase in tyre pressure reduces the contact patch area and lowers the coefficient of friction (making iv incorrect). Higher temperatures soften rubber compounds, which can alter friction characteristics. Since statements (i) and (ii) are undeniably correct, the incorrect statements are (iii) and (iv), corresponding to option D.
Why the other options are wrong
A) Statements (i) and (ii) are correct facts regarding friction reduction. B) Statement (ii) is correct, so it cannot be part of the incorrect statements. C) Only (iii) misses statement (iv), which is definitely incorrect.
Shortcut
High tyre pressure = Smaller contact area = Lower friction (iv is false). Wet & smooth = Lower friction (i & ii are true).
Common mistake
Misreading the question and looking for the correct statements instead of the incorrect statements.
Correct answer: D) (iii) and (iv)