Net Contact Force

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 = μMg

3. 

4. 

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

Q.

When the normal force is doubled, the coefficient of friction is.

1. Doubled.

2. Halved.

3. Not changed.

4. Tripled.

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

Q. A block of mass $5\text{kg}$ is $\left(i\right)$ pushed in case $\left(\text{A}\right)$ and $\left(ii\right)$ pulled in case $\left(\text{B}\right)$, by a force $F=20\text{N}$, making an angle of ${30}^{\circ }$ with the horizontal, as shown in the figures. The coefficient of friction between the block and the floor is $\mu =0.2$. The difference between the accelerations of the block, in case $\left(\text{B}\right)$ and case $\left(\text{A}\right)$ will be
$($Take, $g=10{\text{ms}}^{-2})$

1. $0.4{\text{ms}}^{-2}$
2. $3.2{\text{ms}}^{-2}$
3. $0.8{\text{ms}}^{-2}$
4. $0{\text{ms}}^{-2}$

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

Q. A uniform rod is kept on a smooth horizontal surface, a constant force is applied on the rod in horizontal direction at end 'A'. Find the ratio of energy stored per unit volume at end A to the energy stored per unit volume in the middle of the rod.

1. 2
2. 4
3. 8
4. 6

Q.

A wooden block of 100 kg is about to be published on a floor of coefficient of friction 0.4. What is the magnitude of force of friction on wooden block when it is just pushed?

Q.

The friction coefficient between the table and the block shown in figure (6-E4) is 0.2. Find the tensions in the two strings.

Q. Three blocks of masses $2\text{kg}$, $4\text{kg}$ and $6\text{kg}$ arranged as shown in figure connected by string on a frictionless incline of ${37}^{\circ }$. A force of $120\text{N}$ is applied upward along the incline to the uppermost block. The cords are light. The tensions $T_1$ and $T_2$ in the strings are $(g=10{\text{m/s}}^2,\sin {37}^{\circ }=\frac{3}{5})$

1. $T_1=8\text{N}$
2. $T_2=36\text{N}$
3. $T_1=20\text{N}$
4. $T_2=60\text{N}$

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. Which of the following is correct when a person walks on a rough surface?

1. The normal reaction 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 cylinder having radius $0.4m$, initially rotating (at $t=0$) with ${\omega }_o=54rad.s^{-1}$ is placed on a rough inclined plane with $\theta ={37}^o$ having friction coefficient$\mu =0.5$. The time taken by the cylinder to start pure rolling is ($g=10m{s}^{-2}$)

Q. Why is kinetic friction constant? If friction during motion of an object relative to the ground is a result of continuous formation and breaking of bonds between molecules of ground and the moving body(as explained in Byju's video lectures), then with increase in velocity of the body, it will be difficult for the object to form bonds with the molecules of the ground and hence the kinetic friction should decrease. But why does it have a constant value? What is the explanation of that?

Q.

In the following figure all surfaces are smooth. The system is released from rest, then

1. Acceleration of wedge > g$sin\theta .$

2. Acceleration of $m=g\sqrt{1+2co{s}^2\theta .}$

3. Acceleration of m is g.

4. Acceleration of wedge is g $sin\theta .$

Q. A force is acting on a body of mass $3kg$ kept on a rough horizontal surface. If a friction force of $40N$ is required to keep the body at rest under the action of this external force. Find the contact force acting on the body. (Take $g=10m/s^2$)

1. $30N$
2. $40N$
3. $50N$
4. $100N$

Q. A body of mass $1\text{kg}$ lies on a smooth inclined plane. A horizontal force $F=10\text{N}$ is applied on the block of mass $1\text{kg}$ as shown in figure. If the block remains at rest, then the magnitude of normal reaction on the block is
(Take g $=10{\text{m/s}}^2$)

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

Q.

A block of mass 2 kg is pushed against a rough vertical wall with a force of 40 N, coeffirient of static friction being 0.5 Another horizontal force of 15, is applied on the block iin the direction parallel to the wall. Will the block move? if yes, in which direction? If no, Find the frictional force exerted by the wall on the block.

Q.

A block of mass m can slide freely along the vertical surface of a bigger block of mass M as shown in figure. There is no friction anywhere in the system. The block m is connected to one end of a string whose other end is fixed at point P. The string between $P_1$ and P is horizontal and other parts of the string are vertical. System is released from rest. Find the accelerations of m during their subsequent motion.

1. g

2. mg (m+2m)

3. 

4. 

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. OB
2. OC
3. OD
4. OA

Q. A body of weight $50\text{N}$ is dragged slowly with constant velocity on a horizontal surface as shown in the figure, with a force of $F=28.2\text{N}$ at an angle of ${45}^{\circ }$ with horizontal. The net contact force acting on the body will be

1. $10\sqrt{17}\text{N}$
2. $10\sqrt{13}\text{N}$
3. $10\sqrt{19}\text{N}$
4. $10\sqrt{12}\text{N}$

Q.

Mr.Verma (50 kg) and Mr.Mathur (60 kg) are sitting at the two extremes of a 4 m long boat (40 kg) standing still in water.To discuss a mechanics problem, they come to the middle of the boat.Neglecting friction with water, how far does boat move on the water during the process ?

Q.

A block of weight 50N is pulled along a rough horizontal surface . If coefficient of friction is 1 , then the least possible force that can move the block is..

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 time varying force $F=10\sqrt{2}t$ starts acting on the $3\text{kg}$ block kept on a rough horizontal surface $(\mu =0.2)$ at $t=0$. Find the time when the horizontal motion begins.
(Take $g=10{\text{m/s}}^2$)

1. $\frac{1}{2}\text{s}$
2. $\frac{3}{2}\text{s}$
3. $\frac{5}{2}\text{s}$
4. $\frac{7}{2}\text{s}$

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. 53⁰, 4N

2. 37⁰, 5N

3. 37⁰, 4N

4. None of these

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. may increase or decrease

2. Increase

3. decrease

4. Remain the same

Q. A body of mass $2kg$ is kept on a rough horizontal surface. If ${\mu }_s=0.5$, find the contact force between the body and the surface. Take $g=10m/s^2$.

1. $\text{Zero}$
2. $10N$
3. $10\sqrt{5}N$
4. $20N$

Q.

when a body is at motion then which friction froce is acted upon the body and why?

Q. A block of mass 1 kg is placed on a rough wedge which is fixed on an elevator moving upward with constant velocity 2m/s .The block m is at rest wrt wedge .Net reaction force on the block is