Static Friction

Q.

List the advantages of friction.

Q. The ratio of the limiting force of friction (F) to the normal reaction (R) is known as

1. angle of friction
2. coefficient of static friction
3. coefficient of kinetic friction
4. none of these

Q. If a man is walking on a rough horizontal ground without slipping, then identify the correct statement(s) from the options given below:

1. Frictional force on the man will act in backward direction.
2. Frictional force on the man will act in forward direction.
3. Work done by frictional force on the man will be negative.
4. Work done by frictional force on the man will be $\text{zero}$.

Q.

It is difficult to balance our body when we accidentally slip on the peel of a banana. Explain, why?

Q. Figure shows two blocks connected by a light string placed on the two inclined parts of a triangular structure. The coefficients of static and kinetic friction are $0.28$ and $0.25$ respectively at each of the surfaces. Find the minimum and maximum values of $m$ for which the system remains at rest. (Both in $\text{kg}$)

1. $\frac{9}{8},\frac{32}{9}$
2. $\frac{9}{8},\frac{32}{10}$
3. $\frac{3}{8},\frac{32}{9}$
4. $\frac{3}{8},\frac{32}{10}$

Q. In the figure given below, there are two blocks A and B of weight $20N$ and $100N$ respectively. These are being pressed against a wall by an external force $F$ as shown in figure. If the coefficient of static friction between the blocks is $0.1$ and between block B and the wall is $0.15$, then the frictional force applied by the wall on block B will be

1. $120N$
2. $150N$
3. $100N$
4. $80N$

Q. Choose the incorrect statement from statements given below:

1. Friction is an electromagnetic force.
2. Value of static friction is always greater than kinetic friction.
3. Coefficient of static friction is greater than coefficient of kinetic friction.
4. None of these

Q. Find the friction force between block $A$ and the surface for system at rest given below:
$m_A=9\text{kg},m_B=4\text{kg},{\mu }_s={\mu }_k=0.8$

1. $72\text{N}$
2. $30\text{N}$
3. $40\text{N}$
4. $48\text{N}$

Q. A man standing stationary with respect to a horizontal conveyer belt which is accelerating with $1{\text{m/s}}^2$ as shown in figure. If the coefficient of static friction between man's shoes and the belt is $0.2$, up to what acceleration of the belt can the man continue to be stationary relative to the belt? (Mass of the man $=65\text{kg}$). Take $g=10{\text{m/s}}^2$.

1. $1{\text{m/s}}^2$
2. $2.5{\text{m/s}}^2$
3. $3{\text{m/s}}^2$
4. $2{\text{m/s}}^2$

Q. A board is balanced on a rough horizontal semicircular log. Equilibrium is obtained with the help of addition of a weight on the board, when the board makes an angle $\theta$ with the horizontal. Coefficient of friction between the log and the board is:

1. $\tan \theta$
2. $\cos \theta$
3. $\cot \theta$
4. $\sin \theta$

Q. A force F is applied to a block of mass m at an angle a to the horizontal. If the block is stationary,

1. frictional force is equal to F cos a.
2. frictional force is equal to F sin a.
3. frictional force is equal to mg – F sin a.
4. frictional force is equal to mg + F sin a.

Q. Two masses $m_1=5\text{kg},m_2=10\text{kg}$ connected by an inextensible massless string over a frictionless pulley, are released from rest as shown in the figure. The coefficient of static friction between the horizontal surface and block $m_2$ is $0.15$. The minimum mass $m$ in $\text{kg}$ that should be put on top of $m_2$ to stop the motion is:

1. $23.33\text{kg}$
2. $43.3\text{kg}$
3. $10.3\text{kg}$
4. $18.3\text{kg}$

Q. A lift is moving upwards with a uniform velocity $v$ in which a block of mass $m$ is lying. The frictional force offered by the block, when coefficient of friction is $\mu =0.5$, will be

1. Zero
2. $\frac{mg}{2}$
3. $mg$
4. $2mg$

Q. A block of mass $m$ is at rest on a rough wedge of angle $\theta$ as shown. What is the force exerted by the wedge on the block?

1. $mg\cos \theta$
2. $mg\sin \theta$
3. $mg\tan \theta$
4. $mg$

Q. A block of mass $m$ is placed on a surface with a vertical cross-section represented by the equation $y=\frac{x^3}{6}$. If the coefficient of static friction is $0.5$, the maximum height above the ground at which the block can be placed without slipping is

1. $\frac{1}{3}\text{m}$
2. $\frac{1}{2}\text{m}$
3. $\frac{1}{6}\text{m}$
4. $\frac{2}{3}\text{m}$

Q. A block of mass $100\text{kg}$ is attached to the back of a truck with the help of a spring. The frictional coefficient between the truck and the block is $0.2$ (take ${\mu }_s={\mu }_k)$. Acceleration of the truck is $5{\text{m/s}}^2$ and the spring elongates by a distance of $1\text{cm}$. If the block is just about to slip, what is the force constant of the spring? Take $g=10{\text{m/s}}^2$.

1. $300\text{N/m}$
2. $30000\text{N/m}$
3. $3000\text{N/m}$
4. $1000\text{N/m}$

Q. A board is balanced on a rough horizontal semicircular log. Equilibrium is obtained with the help of addition of a weight on the board, when the board makes an angle $\theta$ with the horizontal. Coefficient of friction between the log and the board is:

1. $\tan \theta$
2. $\cos \theta$
3. $\cot \theta$
4. $\sin \theta$

Q. For the arrangement shown in the figure the tension in the string is
[Given: ${\tan }^{-1}\left(0.8\right)={39}^{\circ }$]

1. $6\text{N}$
2. $6.4\text{N}$
3. $0.4\text{N}$
4. Zero

Q. Find the friction force between block $A$ and the surface for system at rest given below:
$m_A=9\text{kg},m_B=4\text{kg},{\mu }_s={\mu }_k=0.8$

1. $72\text{N}$
2. $30\text{N}$
3. $40\text{N}$
4. $48\text{N}$

Q. Which of the following statement is correct, when a man walks on a rough surface:

1. The frictional force exerted by the surface keeps him moving
2. The force which the man exerts on the floor keeps him moving
3. The reaction of the force which the man exerts on floor keeps him moving
4. None of the above

Q. A heavy uniform chain of length $L$ lies on the top of a horizontal table. If the coefficient of static friction between the chain and the table surface is $0.2$, then the maximum fraction of the length of the chain that can be hung over one edge of the table is:

1. $\frac{L}{6}$
2. $\frac{L}{3}$
3. $\frac{L}{2}$
4. $\frac{L}{4}$

Q. A block of mass $2kg$ is resting on a rough inclined plane of inclination ${30}^{\circ }$. If the coefficient of friction is $0.8$, the resultant contact force between incline and the block is $(g=10m{s}^{-2})$

1. $20N$
2. $10N$
3. $10\sqrt{3}N$
4. None of these

Q. A man standing stationary with respect to a horizontal conveyer belt which is accelerating with $1{\text{m/s}}^2$ as shown in figure. If the coefficient of static friction between man's shoes and the belt is $0.2$, up to what acceleration of the belt can the man continue to be stationary relative to the belt? (Mass of the man $=65\text{kg}$). Take $g=10{\text{m/s}}^2$.

1. $1{\text{m/s}}^2$
2. $2.5{\text{m/s}}^2$
3. $3{\text{m/s}}^2$
4. $2{\text{m/s}}^2$

Q. The tension $T$ in the string in figure is

1. Zero
2. $50N$
3. $35\sqrt{3}N$
4. $(\sqrt{3}-1)50N$

Q.

The coefficient of static friction between the block of 2 kg and the table shown in figure is $\mu$s = 0.2. what should be the maximum value of m so that the blocks do not move? Take g = 10 $m/s^2$. The string and the pulley are light and smooth.

1. 2 kg

2. 1 kg

3. 0.4 kg

4. 0.5 kg

Q. In the figure given below, there are two blocks A and B of weight $20N$ and $100N$ respectively. These are being pressed against a wall by an external force $F$ as shown in figure. If the coefficient of static friction between the blocks is $0.1$ and between block B and the wall is $0.15$, then the frictional force applied by the wall on block B will be

1. $120N$
2. $150N$
3. $100N$
4. $80N$

Q. Two masses $m_1=5\text{kg},m_2=10\text{kg}$ connected by an inextensible massless string over a frictionless pulley, are released from rest as shown in the figure. The coefficient of static friction between the horizontal surface and block $m_2$ is $0.15$. The minimum mass $m$ in $\text{kg}$ that should be put on top of $m_2$ to stop the motion is:

1. $23.33\text{kg}$
2. $43.3\text{kg}$
3. $10.3\text{kg}$
4. $18.3\text{kg}$