Friction

A block is pushed momentarily along a horizontal surface with an initial velocity If is the coefficient of sliding friction between and the surface, the block will come to rest after a time: 

1.
2.
3.
4.

A block of mass is in contact with the cart as shown in the figure. 

The coefficient of static friction between the block and the cart is The acceleration of the cart that will prevent the block from falling satisfies:
1.
2.
3.
4.

A gramophone record is revolving with an angular velocity $\mathrm{\backslash omega}$. A coin is placed at a distance r from the centre of the record. The static coefficient of friction is $\mathrm{\backslash mu}$. The coin will revolve with the record if:

1. $r=\mathrm{\backslash mu}g{\mathrm{\backslash omega}}^2$

2. $r<\frac{{\mathrm{\backslash omega}}^2}{\mathrm{\backslash mu}g}$

3. $r\backslash leq\frac{\mathrm{\backslash mu}g}{{\mathrm{\backslash omega}}^2}$

4. $r\backslash geq\frac{\mathrm{\backslash mu}g}{{\mathrm{\backslash omega}}^2}$

The upper half of an inclined plane of inclination is perfectly smooth while the lower half is rough. A block starting from rest at the top of the plane will again come to rest at the bottom if the coefficient of friction between the block and the lower half of the plane is given by:
1.
2.
3.
4.

A plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches the box starts to slip and slide down the plank in The coefficients of static and kinetic friction between the box and the plank will be, respectively:

1.	and	2.	and
3.	and	4.	and

Which one of the following statements is incorrect?

1.	Rolling friction is smaller than sliding friction.
2.	The limiting value of static friction is directly proportional to the normal reaction.
3.	Frictional force opposes the relative motion.
4.	The coefficient of sliding friction has dimensions of length.

Calculate the acceleration of the block and trolly system shown in the figure. The coefficient of kinetic friction between the trolly and the surface is
( the mass of the string is negligible and no other friction exists)

1.		2.
3.		4.

Calculate the maximum acceleration of a moving car so that a body lying on the floor of the car remains stationary. The coefficient of static friction between the body and the floor is . (take ms^–2)

1.	ms–2	2.	ms–2
3.	ms–2	4.	ms–2

There are two inclined surfaces of equal length and same angle of inclination with the horizontal. One of them is rough and the other is perfectly smooth. A given body takes times as much time to slide down on rough surface than on the smooth surface. The coefficient of kinetic friction between the object and the rough surface is close to:

1.		2.
3.		4.