Q: State two advantages and disadvantages of friction.

Advantages of friction: \$1.\$ Friction enables us to walk freely.\$2.\$ It helps to support ladder against wall.\$3.\$ It becomes possible to transfer one form of energy to another.\$4.\$ Objects can be piled up without slipping.\$5.\$ Breaks of vehicles work due to friction.Disadvantages of friction:\$1.\$It always resists the motion, so extra energy is required to overcome it.\$2.\$It causes wear and tear of machines.\$3.\$It decreases the life expectancy of moving parts of vehicles.\$4.\$Since friction is very useful in some cases while harmful in some cases, friction is called a necessary evil.

Q: Mention the methods used to decrease friction

\$\textbf{Cause of Friction: }\$To Identify methods of reducing friction, we first have to understand what is the cause of friction. There are two reasons behind friction:Whenever two surfaces come in contact, then the temporary bond's start forming between them, which resist the movement between the surfaces. Higher the area of contact, larger the number of bonds, higher the value of friction force.The abnormality/Roughness of the surface, more rough the surface is, higher the friction.Value of friction force is proportional to the Normal contact force. Higher the Normal force, larger is the friction\$\textbf{Methods for Reduction friction: }\$Make the surfaces little more smoother. Rough surfaces produce more friction and smooth surfaces reduce friction. Note: Making surface highly smooth will also increase the friction, as large number of bonds will form then.Lubrication is another way to make a surface smoother. A lubricant is a slippery substance designed to reduce the friction between surfaces. Make the object more streamlined. A streamline shape is one that allows air or water to flow around it easily, offering the least resistance.Reduce the Normal force acting between the surfaces in contact. The stronger the Normal force acting on the surfaces, the higher the friction.Reduce the contact between the surfaces, so that less number of bonds will be formed. Spheres are the best shape for reducing friction because very little of a spherical object is in contact with the other surface.

Q: A marble block of mass 2kg lying on ice when given a velocity of \$6m{s}^{-1}\$ is stopped by friction in 10s. Then the coefficient of friction is ( Take \$g=10ms^{-2}\$)

\$a=\mu g = \dfrac{6}{10}\$ [using v=u+at]\$\Rightarrow \mu = \dfrac{6}{10 \times g}= \dfrac{6}{10 \times 10}=0.06\$

Q: A block weighing 20N rests on a horizontal surface. The coefficient of static friction between the block and surface is 0.4 and the coefficient of kinetic friction is 0.20.a. How much is the friction force exerted on the block?b. How much will the friction force be if a horizontal force 5N is exerted on the block?c. What is the minimum force that will start the block in motion?d. What is the minimum force that will keep the block in motion once it has been started?e. If the horizontal force is 10N, what is the friction force?

a. \$F_{fric} = \mu_s W = 0.4*20 = 8N \$b. Since \$F_{applied} F_{staticfric}\$ motion started.\$F > F_{kineticfric}\$ hence motion continues.\$F_{fric} = 4N\$

Q: A block of mass \$1\ kg\$ lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is \$0.6\$. What is the force of friction on the block if the acceleration of the truck is \$5\ m/s^{2}\$ ?(Take \$g=10\ m/s^{2}\$)

Maximum frictional force acting \$= \mu mg = 0.6 \times 1 \times 10 = 6 \; N\$Pseudo force acting on the body \$= ma = 1 \times 5 = 5 \; N\$\$\because\$ pseudo force \$<\$ frictional forceThe frictional force acting is only \$5 \; N\$.

Q: A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

We know frictional force \$f=\mu N\$ where N=normal force=mgGiven sliding friction\$\mu=0.25\$ Thus, \$f=0.25\times 50\times 10=125 N\$Hence \${F}_{net}={F}_{app}-f=575-125=450 N\$Also we know Force\$F=ma\$\$a=\dfrac{450}{50}=9 m/{s}^{2}\$

Q: A block of weight \$100\$ \$N\$ is lying on a rough horizontal surface. If coefficient of friction \$\cfrac{1}{\sqrt{3}}\$. The least possible force that can move the block is

We have formula\$F_{min}-\mu N\$Here \$\mu=\$ coefficient of function \$=\dfrac {1}{\sqrt 3}\$and \$N=100\ N\$So \$F_{min}=\dfrac {100}{\sqrt 3}\$ ans

Q: Which one of the following statements is incorrect?

Sliding friction id given by F = \$\mu\$.N or \$\mu=\dfrac{F}{N}\$Force and Normal reaction both are given by newton, so the \$\mu\$ is dimensionless. Therefore, statement C is wrong.

Question 1

State two advantages and disadvantages of friction.

Accepted Answer

Advantages of friction: $1.$ Friction enables us to walk freely.$2.$ It helps to support ladder against wall.$3.$ It becomes possible to transfer one form of energy to another.$4.$ Objects can be piled up without slipping.$5.$ Breaks of vehicles work due to friction.Disadvantages of friction:$1.$It always resists the motion, so extra energy is required to overcome it.$2.$It causes wear and tear of machines.$3.$It decreases the life expectancy of moving parts of vehicles.$4.$Since friction is very useful in some cases while harmful in some cases, friction is called a necessary evil.

Question 2

Mention the methods used to decrease friction

Accepted Answer

$\textbf{Cause of Friction: }$To Identify methods of reducing friction, we first have to understand what is the cause of friction. There are two reasons behind friction:Whenever two surfaces come in contact, then the temporary bond's start forming between them, which resist the movement between the surfaces. Higher the area of contact, larger the number of bonds, higher the value of friction force.The abnormality/Roughness of the surface, more rough the surface is, higher the friction.Value of friction force is proportional to the Normal contact force. Higher the Normal force, larger is the friction$\textbf{Methods for Reduction friction: }$Make the surfaces little more smoother. Rough surfaces produce more friction and smooth surfaces reduce friction. Note: Making surface highly smooth will also increase the friction, as large number of bonds will form then.Lubrication is another way to make a surface smoother. A lubricant is a slippery substance designed to reduce the friction between surfaces. Make the object more streamlined. A streamline shape is one that allows air or water to flow around it easily, offering the least resistance.Reduce the Normal force acting between the surfaces in contact. The stronger the Normal force acting on the surfaces, the higher the friction.Reduce the contact between the surfaces, so that less number of bonds will be formed. Spheres are the best shape for reducing friction because very little of a spherical object is in contact with the other surface.

Question 3

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.Choose the correct arrangement.

Accepted Answer

Sliding friction is the force of friction, below two objects, when one of them is sliding over the surface of the other. The force of sliding friction between them is a little smaller than static friction between them. Between the same two surfaces, once motion is started the friction becomes slightly less than maximum static force rolling friction - force of friction that comes into play when one body rolls over the surface of another body.It is more convenient to roll then to slide an object once the surface of other Hence, static friction > sliding friction > Rolling friction.

Question 4

Starting from rest ,a body slides down a 45$^{o}$ inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

Accepted Answer

Case (1) When there is no friction,    From newton's second law,     F=ma                                                 $\Rightarrow mg\sin { \theta }= m{ a }_{ 1 }$                                                $\Rightarrow {a }_{ 1}= g\sin { \theta  } $Now, as body starts from rest so initial velocity (u)=0 m/s.Let, body travels 'x' distance in ${t}_{1}$ time,So from equation of motion,                 $x=ut+\frac { 1 }{ 2 } a{ t }^{ 2 }$            $\Rightarrow x=\frac { 1 }{ 2 } { a }_{ 1 }{ { t }_{ 1 } }^{ 2 }$            $\Rightarrow { t }_{ 1 }=\sqrt { \frac { 2x }{ { a }_{ 1 } }  } =\sqrt { \frac { 2x }{ g\sin { \theta  }  }  } $Case (2) When there is friction,    From newton's second law,     F=ma                                                 $\Rightarrow mg\sin { \theta  } -\mu mg\cos { \theta  } =m{ a }_{ 2 }$                                                $\Rightarrow { a }_{ 2 }=g\sin { \theta  } -\mu g\cos { \theta  } $Now, as body starts from rest so initial velocity (u)=0 m/s.Let, body travels 'x' distance in ${t}_{2}$ time,So from equation of motion,                 $x=ut+\frac { 1 }{ 2 } a{ t }^{ 2 }$            $\Rightarrow x=\frac { 1 }{ 2 } { a }_{ 2 }{ { t }_{ 2 } }^{ 2 }$            $\Rightarrow { t }_{ 2 }=\sqrt { \frac { 2x }{ { a }_{ 1 } }  } =\sqrt { \frac { 2x }{ g\sin { \theta  } -\mu g\cos { \theta  }  }  }  $It is given that ${t}_{2}=2{t}_{1}$So,                   $\sqrt { \frac { 2x }{ g\sin { \theta  } -\mu g\cos { \theta  }  }  } =2\sqrt { \frac { 2x }{ g\sin { \theta  }  }  }  $Now, substituting $\theta=45$ and solving above equation we get,                         $\sqrt { \frac { 1 }{ 1-\mu  }  } =2$                         $\mu =\frac { 3 }{ 4 } =0.75$

Question 5

A marble block of mass 2kg lying on ice when given a velocity of $6m{s}^{-1}$ is stopped by friction in 10s. Then the coefficient of friction is ( Take $g=10ms^{-2}$)

Accepted Answer

$a=\mu g = \dfrac{6}{10}$ [using v=u+at]$\Rightarrow \mu = \dfrac{6}{10 \times g}= \dfrac{6}{10 \times 10}=0.06$

Question 6

A block weighing 20N rests on a horizontal surface. The coefficient of static friction between the block and surface is 0.4 and the coefficient of kinetic friction is 0.20.
a. How much is the friction force exerted on the block?
b. How much will the friction force be if a horizontal force 5N is exerted on the block?
c. What is the minimum force that will start the block in motion?
d. What is the minimum force that will keep the block in motion once it has been started?
e. If the horizontal force is 10N, what is the friction force?

Accepted Answer

a. $F_{fric} = \mu_s W = 0.4*20 = 8N $b. Since $F_{applied} < F_{fric}$$F_{fric} = 5N$c.  Minimum force required to start the motion $F = F_{static fric} = 8N$d.  Minimum force required to start the motion$F = F_{kineticfric} = \mu_kW = 0.2*20 = 4N$e. $F > F_{staticfric}$ motion started.$F > F_{kineticfric}$ hence motion continues.$F_{fric} = 4N$

Question 7

A block of mass $1\ kg$ lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is $0.6$. What is the force of friction on the block if the acceleration of the truck is $5\ m/s^{2}$ ?(Take $g=10\ m/s^{2}$)

Accepted Answer

Maximum frictional force acting $= \mu mg = 0.6 \times 1 \times 10 = 6 \; N$Pseudo force acting on the body $= ma = 1 \times 5 = 5 \; N$$\because$ pseudo force $<$ frictional forceThe frictional force acting is only $5 \; N$.

Question 8

A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

Accepted Answer

We know frictional force $f=\mu N$ where N=normal force=mgGiven sliding friction$\mu=0.25$ Thus, $f=0.25\times 50\times 10=125 N$Hence ${F}_{net}={F}_{app}-f=575-125=450 N$Also we know Force$F=ma$$a=\dfrac{450}{50}=9 m/{s}^{2}$

Question 9

A block of weight $100$ $N$ is lying on a rough horizontal surface. If coefficient of friction $\cfrac{1}{\sqrt{3}}$. The least possible force that can move the block is

Accepted Answer

We have formula$F_{min}-\mu N$Here $\mu=$ coefficient of function $=\dfrac {1}{\sqrt 3}$and $N=100\ N$So $F_{min}=\dfrac {100}{\sqrt 3}$ ans

Question 10

Which one of the following statements is incorrect?

Accepted Answer

Sliding friction id given by F = $\mu$.N    or   $\mu=\dfrac{F}{N}$Force and Normal reaction both are given by newton, so the $\mu$ is dimensionless. Therefore, statement C is wrong.

Revise with Concepts

What is Rolling Friction?

Quick Summary With Stories

Rolling friction

State two advantages and disadvantages of friction.

Mention the methods used to decrease friction

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.
Choose the correct arrangement.

Starting from rest ,a body slides down a 45 $^{o}$ inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

A marble block of mass 2kg lying on ice when given a velocity of $6 m s^{- 1}$ is stopped by friction in 10s. Then the coefficient of friction is ( Take $g = 10 m s^{- 2}$ )

A block of mass $1 k g$ lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is $0.6$ . What is the force of friction on the block if the acceleration of the truck is $5 m / s^{2}$ ?
(Take $g = 10 m / s^{2}$ )

A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

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

Which one of the following statements is incorrect?

Revise with Concepts

What is Rolling Friction?

Quick Summary With Stories

Rolling friction

State two advantages and disadvantages of friction.

Mention the methods used to decrease friction

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below. Choose the correct arrangement.

Starting from rest ,a body slides down a 45o inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

A marble block of mass 2kg lying on ice when given a velocity of 6ms−1 is stopped by friction in 10s. Then the coefficient of friction is ( Take g=10ms−2)

A block of mass 1 kg lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is 0.6. What is the force of friction on the block if the acceleration of the truck is 5 m/s2 ? (Take g=10 m/s2)

A 50 kg crate is being pushed across a horizontal floor by a horizontal force of 575 N. If the coefficient of sliding friction is 0.25, what is the acceleration of the crate ?

A block of weight 100 N is lying on a rough horizontal surface. If coefficient of friction 3​1​. The least possible force that can move the block is

Which one of the following statements is incorrect?

Four children were asked to arrange forces due to rolling, static and sliding frictions in a decreasing order. Their arrangements are given below.
Choose the correct arrangement.

Starting from rest ,a body slides down a 45 $^{o}$ inclined plane in twice the time takes to slide down the same distance in the absence of friction .The coefficient of friction between the body and inclined plane is

A marble block of mass 2kg lying on ice when given a velocity of $6 m s^{- 1}$ is stopped by friction in 10s. Then the coefficient of friction is ( Take $g = 10 m s^{- 2}$ )

A block of mass $1 k g$ lies on a horizontal surface in a truck, the coefficient of static friction between the block and the surface is $0.6$ . What is the force of friction on the block if the acceleration of the truck is $5 m / s^{2}$ ?
(Take $g = 10 m / s^{2}$ )

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