Q. A coin of mass 10 g is placed over a book of length 50 cm. the coin is on the verge of sliding when one end of the book is lifted to 10 cm up. The coefficient of static friction between the book and the coin is
A) 1.0
B) 0.4
C) 0.3
D) 0.2
Explanation
(d) The coin will not slide if
[image:5_image185.emf]
$mg\sin{\theta = \mu\ R}$
$ie,\ \ \ mg\sin{\theta = \mu\ mg\cos\theta}$ ($as\ R = mg\cos{\theta)}$
$ie,\ \tan{\theta = \mu}$
$Here,\ \ \tan{\theta = \frac{10}{\sqrt{(50)^{2} - (10)^{2}}} = 0.2}$
$\therefore\ \ \ \ \mu = 0.2$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.