Net Contact Force

Q.

A body of mass 400g slides on a rough horizontal surface. If the frictional force is 3.0 N, find (a) the angle made by the contact force on the body with the vertical and (b) the magnitude of the contact force. Take g = 10$\frac{m}{s^2}$

1. 4N

2. 5N

3. 4N

4. None of these

Q. A bob of mass m is suspended from the ceiling of a train moving with an acceleration a as shown in figure. Find the angle $\theta$ in equilibrium position.

1. 
2. 
3. 
4. 

Q. In which of the following cases is the contact force between $A$ and $B$ is maximum. If mass of each block is $1\text{kg}$ and assume all surfaces to be smooth :-

1. 
2. 
3. 
4. 

Q.

Given in the figure are two blocks A and B of weight 20 N and 100 N, respectively. These are being pressed against a wall by a force F as shown. If the coefficient of friction between the blocks is 0.1 and between block B and the wall is 0.15, the frictional force applied by the wall on block B is:

1. 120 N

2. 80 N

3. 100 N

Q.

A body of mass M is kept on a rough horizontal surface (friction coefficient = $\mu$). A person is trying to pull the body by applying a horizontal force but the body is not moving. The force by the surface on the body is F, where

1. F = Mg

2. F = $\mu$Mg

3. Mg $\le$ F $\le$ Mg $\sqrt{1+{\mu }^2}$

4. Mg $\ge$ F $\ge$ Mg $\sqrt{1+{\mu }^2}$

Q. A block of mass $m$ is at rest with respect to a rough inclined plane kept in an elevator moving up with an acceleration $‘a^{\prime }$. Which of the following statements is correct?

1. $\text{The contact force between block and the inclined plane is parallel to the incline.}$
2. $\text{The contact force between block and the inclined plane is of magnitude}m(g+a)$
3. $\text{The contact force between block and the inclined plane is perpendicular to the incline}$
4. $\text{The contact force between block and the inclined plane is of magnitude}mg\cos \theta$

Q.

A bob is hanging over a pulley inside a car through a string. The second end of the string is in the hand of a person standing in the car. The car is moving with constant acceleration 'a' directed horizontally as shown in figure. Other end of the string is pulled with constant acceleration 'a' vertically (with respect to train). The tension in the string is equal to

1. m(g + a)

2. 

3. 

4. 

Q.

In a situation the contact force by a rough horizontal surface on a body placed on it has constant magnitude. If the angle between this force and the vertical is decreased, the frictional force between the surface and the body will

1. Increase

2. decrease

3. Remain the same

4. may increase or decrease

Q.

What is coefficient of Kinetic friction ?

Q.

Laws of Limiting and Kinetic Friction

Q. In case of frictionless surfaces, does normal reaction mean contact force ? If friction is there then it is the resul†an t of frictional force and normal reaction. Is it the same contact force in both cases?

Q.

A body of mass M is kept on a rough horizontal surface (friction coefficient = $\mu$). A person is trying to pull the body by applying a horizontal force but the body is not moving. The force by the surface on A is F, where

1. F = Mg

2. F = Mg

3. Mg F Mg

4. Mg F Mg

Q. Find the direction of the reaction force on the block for the figure shown.

1. $\text{Perpendicular to the plane}$
2. $\text{At an angle to the plane}$
3. $\text{Up the plane}$
4. $\text{Down the plane}$

Q.

A body of mass M is kept on a rough horizontal surface (friction coefficient = $\mu$). A person is trying to pull the body by applying a horizontal force but the body is not moving. The force by the surface on the body is F, where

1. F = Mg

2. F = $\mu$Mg

3. Mg $\le$ F $\le$ Mg $\sqrt{1+{\mu }^2}$

4. Mg $\ge$ F $\ge$ Mg $\sqrt{1+{\mu }^2}$

Q. A block of mass $2\text{kg}$ rests on a rough inclined plane making an angle of ${30}^{\circ }$ with the horizontal. The coefficient of static friction between the block and the plane is $0.7$. The frictional force on the block is

1. $9.8\text{N}$
2. $0.7\times 9.8\times \sqrt{3}\text{N}$
3. $9.8\times \sqrt{3}\text{N}$
4. $0.7\times 9.8\text{N}$

Q. A body of mass $10kg$ lies on a rough inclined plane of inclination $\theta ={37}^{\circ }$ with the horizontal. When the force of $30N$ is applied on the block parallel to and upward the plane, the contact force by the plane on the block is nearby along

1. OA
2. OB
3. OC
4. OD

Q. Block is pushed from bottom of inclined plane with speed 6 m/s as shown in figure, find time after which the block will return to the initial position?

1. t=4.2 s
2. t=3.6s
3. t=12.8 s
4. Block will not return

Q. A block of mass $m$ is at rest with respect to a rough inclined plane kept in an elevator moving up with an acceleration $‘a^{\prime }$. Which of the following statements is correct?

1. $\text{The contact force between block and the inclined plane is parallel to the incline.}$
2. $\text{The contact force between block and the inclined plane is of magnitude}m(g+a)$
3. $\text{The contact force between block and the inclined plane is perpendicular to the incline}$
4. $\text{The contact force between block and the inclined plane is of magnitude}mg\cos \theta$

Q. what happens to the coefficient of friction when the normal reaction is halved? give reason for the answer

Q. The angle between the normal reaction and the resultant of limiting force of friction and normal reaction