A box of mass 6 k g rests upon an inclined plane. The inclination of the plane to the horizontal direction is gradually increased. It is found that when the slope of the plane is 2 in 3 , the box starts sliding down the plane. Find the co-efficient of friction between the box and the plane. What force applied to the box parallel to the plane will make it move up the plane ? g = 9 . 8 m s - 2 .

Given the mass of the body m = 6 kg The slope of the plane at the equilibrium = 2 3 At equilibrium, the dow nward force = upward force, Refer to the figure, we have, mg sin θ = F = μmg cos θ or μ = tanθ = 2 3 = 0 . 66 The force required to move the body upwards , f = F down + F up = 2 F down as both are equal = 6 × 9 . 8 ( 2 × 2 13 ) = 66 . 66 N .

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A man holds a book of mass $2 k g$ by pressing his two hands towards each other horizontally on two sides of the book. If the minimum force to be applied by each hand is $5 k g$ . wt. then calculate the coefficient of friction between his hand and the book.

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Important Questions on Equilibrium of Concurrent Forces and Friction

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11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 19

A man weigh

80 k g

. What is the greatest weight he can pull along a horizontal floor by a horizontal rope, if the coefficient of friction between his shoe soles and the floor is

0.5

and that between the weight and the floor is

0.4

. The tension in the rope is

x N

. Calculate the value of

x

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A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 1

A small body is gently laid on a horizontal conveyor belt moving with a speed of

4.5 m s^{- 1}

. The coefficient of friction between the body and the belt

0.45

. The body moves

x m

before coming to rest. Find the value of

x

correct to one decimal place?

g = 9.8 m s^{- 2}

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11th West Bengal Board

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A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 2

A disc is sliding down an inclined plane, inclined at an angle

θ

with the horizon, with uniform velocity. If the disc is pushed up the plane with a velocity

u

, the disc will come to rest after describing a distance

u^{2} / k g \sin θ

and will not come down the plane again. Find the value of

k

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A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 3

A body is sliding down a rough inclined plane of inclination

θ

for which the co-efficient of friction is of the form

μ (x) = k x

where

x

stands for the distance moved by the body down the plane. Show that the force on the body will be zero at a distance

x_{o} = \frac{\tan θ}{k}

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A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 4

A box of mass

6 k g

rests upon an inclined plane. The inclination of the plane to the horizontal direction is gradually increased. It is found that when the slope of the plane is

2

3

, the box starts sliding down the plane. Find the co-efficient of friction between the box and the plane. What force applied to the box parallel to the plane will make it move up the plane ?

g = 9.8 m s^{- 2}

HARD

11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 5

A force of $3 t^{2}$ is applied on a body of mass $10 k g$ . A constant frictional force of $3.2 k g f$ acts on the body. What is the velocity of the body after $5$ seconds if the initial velocity is $10 m s^{- 1}$ . Given $g = 10 m s^{- 2}$ .

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11th West Bengal Board

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A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 6

A block slides with uniform speed down an inclined plane which is inclined at an angle of

20^{0}

to the horizontal. If the same block is projected up the plane with an initial velocity of

2 m s^{- 1}

, how far up the plane would it travel before it comes to rest? Will the block slide down the plane again ?

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11th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART I : CLASS 11>Chapter 7 - Equilibrium of Concurrent Forces and Friction>EXERCISE>Q 7

How high can a particle rest inside a hollow sphere of radius

r

, if the co-efficient Of friction be

\frac{1}{\sqrt{3}}

A man holds a book of mass 2 kg by pressing his two hands towards each other horizontally on two sides of the book. If the minimum force to be applied by each hand is 5 kg. wt. then calculate the coefficient of friction between his hand and the book.

Important Questions on Equilibrium of Concurrent Forces and Friction

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A man holds a book of mass $2 k g$ by pressing his two hands towards each other horizontally on two sides of the book. If the minimum force to be applied by each hand is $5 k g$ . wt. then calculate the coefficient of friction between his hand and the book.