Friction and Surface Area of the Object

Q. Which of the following statements is false about static friction?

1. It is a self-adjusting force
2. It depends on the external force applied on the body
3. It depends on the area of contact
4. It depends on the surfaces of contact.

Q. A car moves on a horizontal track of radius $r$, the speed increasing constantly at rate $\frac{dv}{dt}$$=a$. The coefficient of friction between road and tyre is $\mu$. Find the speed at which the car will skid.

1. ${\left[({\mu }^2{g}^2+a^2)r^2\right]}^{1/4}$
2. $\sqrt{\mu gr}$
3. $\sqrt{ar}$
4. ${\left[({\mu }^2{g}^2-a^2)r^2\right]}^{1/4}$

Q. Which of the following statements is false about static friction?

1. It depends on the external force applied on the body
2. It depends on the surfaces of contact.
3. It is a self-adjusting force
4. It depends on the area of contact

Q. 2 books of 1 Kg each are placed on a table. The coefficient of static friction between the books and the book and the table is µ. Find the minimum force F applied to the lower book so that there occurs slip between both the books.