Finding Friction's Direction

Q.

List ten examples of friction in our daily life.

Q.

Define angle of friction.

Q.

What are the advantages of friction?

Q. The force required to just move a body up an inclined plane is double the force required to just prevent it from sliding down. If $\theta$ is the angle of friction and $\varphi$ is the angle which the plane makes with horizontal, then:

1. $tan\varphi =2tan\theta$
2. $tan\varphi =3tan\theta$
3. $tan\varphi =tan\theta$
4. $tan\theta =3tan\varphi$

Q. A block of mass $m$ is on an inclined plane of angle $\theta$. The coefficient of friction between the block and the plane is $\mu$ and $\tan \theta >\mu$. The block is held stationary by applying a force $P$ parallel to the plane. The direction of force pointing up the plane is taken to be positive. As $P$ is varied from $P_1=mg(\sin \theta -\mu \cos \theta )$ to $P_2=mg(\sin \theta +\mu \cos \theta )$, the frictional force $f$ versus $P$ graph will look like

1. 
2. 
3. 
4. 

Q. $\text{Statement 1:}$ A rigid disc rolls without slipping on a fixed rough horizontal surface with uniform angular velocity, then the acceleration of the lowest point on the disc is zero.

$\text{Statement 2:}$ For a rigid rolling without slipping on a fixed rough horizontal surface, the velocity at the lowest point on the disc is always zero.

1. Statement $1$ is false and statement $2$ is true.
2. Statement $1$ is true and statement $2$ is false.
3. Both statements are true and statement $2$ is the correct explanation of statement $1$.
4. Both statements are true and statement $1$ is the correct explanation of $2$.

Q.

State three applications of the universal law of gravitation?

Q.

Name the scientist who gave the universal law of gravitation.

Q. Work done by static friction on a block

1. Must be negative
2. Must be positive
3. Must be zero
4. May be zero

Q. Two blocks of masses $m_1$ and $m_2$ are connected with a massless unstretched spring and placed over a plank moving with an acceleration $a$ as shown in the figure. The coefficient of friction between the blocks and the platform is $\mu$.

1. Spring will be stretched if $a>\mu g$
2. Spring will be compressed if $a\le g$
3. Spring will neither be stretched nor be compressed for $a\le g$
4. Spring will be in its natural length under all conditions

Q.

A block of weight 100 N is lying on a rough horizontal surface .it's coefficient of friction is $\frac{1}{\sqrt{3}}$ the least possible force that can move the block is?

Q. Two blocks of masses $m_1$ and $m_2$ are connected through a massless inextensible string. Block of mass $m_1$ is placed on the fixed rigid inclined surface, while the block of mass $m_2$ is hanging at the other end of the string, which is passing through a fixed massless frictionless pulley shown in figure. The coefficient of static friction between the block and the inclined plane is 0.8. The system of masses $m_1$ and $m_2$ is released from rest. Take $g=10m{s}^{-2}$

1. The tension in the string is 20 N after releasing the system.
2. The contact force by the inclined surface on the block is along normal to the inlined surface.
3. the magnitude of the contact force by the inclined surface on the block $m_1$ is $20\sqrt{3}\text{N}$.
4. None of these.

Q. A block of mass $M$ is sliding down on a inclined plane. The co-efficient of static and kinetic friction between the block and the inclined plane is ${\mu }_s$ and ${\mu }_k$ respectively. Then friction force acting on the block is

1. ${\mu }_k(F+Mg)\sin \theta$
2. ${\mu }_k(F+Mg)\cos \theta$
3. ${\mu }_{s}Mg\cos \theta$
4. $(Mg+F)\tan \theta$

Q.

A body of mass $10\text{kg}$ lies on a rough inclined plane of inclination $\theta ={\sin }^{-1}\frac{3}{5}$ with the horizontal. When a force of $30\text{N}$ is applied on the block parallel to and upward the plane, the total reaction by the plane on the block is nearly along (take $g=10m{s}^{-2}$)

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

Q. A box of mass $\text{8 kg}$ is placed on a rough inclined plane of angle $\theta$. Its downward motion can be prevented by applying an upward pull $F$ and it can be made to slide upwards(constant speed) by applying a force $2F$. The coefficient of friction between the box and the inclined plane is

1. $\frac{\tan \theta }{3}$
2. $3\tan \theta$
3. $\tan \frac{\theta }{3}$
4. $2\tan \theta$

Q.

A box is gently placed on a horizontal conveyer belt moving with a speed of $4m{s}^{-1}$. If the coefficient of friction between the box and the belt is 0.8, through what distance will the block slide without slipping? Take g = $10m{s}^{-2}$

Q.

Two blocks of masses $m_1=m_2=m$ are connected by a string of negligible mass which passes over a frictionless pulley fixed on the top of an inclined plane as shown in the figure. When the angle of inclination $\theta ={30}^{\circ }$, the mass $m_1$ just begins to move up the inclined plane. What is the coefficient of friction between block$m_1$ and the inclined plane?

1. $\frac{1}{\sqrt{2}}$

2. $\frac{1}{2\sqrt{2}}$

3. $\frac{1}{\sqrt{3}}$

4. $\frac{1}{2\sqrt{3}}$

Q. A small block of mass of $0.1\text{kg}$ lies on a fixed inclined plane $PQ$ which makes an angle $\theta$ with the horizontal. A horizontal force of $1\text{N}$ acts on the block as shown in the figure. The block remains stationary if (take $g=10{\text{m/s}}^2$)

1. $\theta ={45}^{\circ }$
2. $\theta >{45}^{\circ }$, and a frictional force acts on the block towards $Q$
3. $\theta >{45}^{\circ }$, and a frictional force acts on the block towards $P$
4. $\theta <{45}^{\circ }$, and a frictional force acts on the block towards $Q$

Q.

A force of 98N is just able to move a block of mass 20kg on a rough horizontal surface.

1.Calculate the coeeficent of friction

and the angle

Q. Why newton's law of gravitation strictly holds for point masses only?

Q. The frictional force acts in the direction on a drop of rain falling down with constant speed.

1. upward
2. downward
3. forward

Q. A rod is inserted between two boxes as shown in figure. A horizontal force F is applied at the upper end of rod. Then

1. both A and B will move simultaneously.
2. cant be predicted.
3. box A will move first.
4. box B will move first.

Q. A horizontal force F pulls a 10kg carton across the floor at a constant speed. If the coefficient of sliding friction between carton and floor is 0.50, the work done by F in moving the carton through 5m is

Q. $\text{Assertion}$: Kepler's laws of planetary motion are a consequence of Newton's law of gravitation.

$\text{Reason}$: Kepler's laws can be derived using Newton's law of gravitation.

1. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
2. Both assertion and Reason are true, but Reason is not the correct explanation of Assertion.
3. Assertion is true, but Reason is false.
4. Assertion is false, but Reason is true.

Q.

A block of mass 15 kg is placed on a long trolley. The coefficient of static friction between the block and the trolley is 0.18. The trolley accelerates from rest with 0.5 m s^–2 for 20 s and then moves with uniform velocity. Discuss the motion of the block as viewed by (a) a stationary observer on the ground, (b) an observer moving with the trolley.

Q. Two blocks of masses $m_1$ and $m_2$ are connected through a massless inextensible string. Block of mass $m_1$ is placed at the fixed rigid inclined surface while the block of mass $m_2$ hanging at the other end of the string, which is passing through a fixed massless frictionless pulley shown in figure. The coefficient of static friction between the block and the inclined plane is 0.8. The system of masses $m_1$ and $m_2$ is released from rest. (Take $g=10{\text{m/s}}^2)$

1. The tension in the string is $20N$ after releasing the system
2. The contact force by the inclined surface on the block is along normal to the inclined surface
3. The magnitude of contact force by the inclined surface on the block $m_1$ is $20\sqrt{3}N$
   
4. Frictional force between $4\text{kg}$ and inclined plane is zero

Q. Two spheres of masses m and M are situated in air and the gravitational force between them is F. The space around the masses is now filled with a liquid of specific gravity 3. The gravitational force will now be?

Q. Which external force is acting when a man walks?

Q.

What is Friction? Explain with an example

Q. State and explain the laws of limits friction.