HARD

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In the figure masses $m_{1}$ _, $m_{2}$ and $M$ are $20 kg$ , $5 kg$ and $50 kg$ respectively. The coefficient of friction between $M$ and ground is zero. The coefficient of friction between $m_{1}$ and $M$ and that between $m_{2}$ and ground is $0.3$ . The pulleys and the strings are massless. The string is perfectly horizontal between $P_{1}$ and $m_{1}$ and also between $P_{2}$ and $m_{2}$ .

Let the magnitude of the force of friction between $m_{1}$ and $M$ be $f_{1}$ and that between $m_{2}$ and ground be $f_{2}$ . For a particular force $F$ it is found that $f_{1} = 2 f_{2}$ . What is $F$ , tension in the string and accelerations of the masses?

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Important Questions on Laws of Motion

MEDIUM

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A small spherical droplet of density

d

is floating exactly half immersed in a liquid of density

ρ

and surface tension

T .

The radius of the droplet is (take note that the surface tension applies an upward force on the droplet):

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A block A of mass 4 kg is placed on another block B of mass 5 kg, and the block B rests on a smooth horizontal table. If the minimum force that can be applied on A so that both the blocks move together is 12 N, the maximum force that can be applied on B for the blocks to move together will be :

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

Which one of the following statement is correct?

HARD

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A block of mass

100 kg

attached to a massless rope and the second end of the rope is pulled up by

2

men along a rough inclined plane of coefficient of friction

0.2

inclined at

37 °

with the horizontal. If they exert their maximum force for the block to just start moving up, the force exerted by each of them is, (Acceleration due to gravity

= 10 m s^{- 2}, \tan 37 ° ≃ 0.75

)

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A rectangular film of liquid is extended from

(4 cm \times 2 cm)

(5 cm \times 4 cm)

. If the work done is

3 \times 10^{- 4} J

, the value of the surface tension of the liquid is

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A wire of length

10 cm

is gently placed horizontally on the surface of water having a surface tension of

75 \times 10^{- 3} N m^{- 1}

. What force is required to just pull up the wire from the water surface?

HARD

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

In the figure, a ladder of mass m is shown leaning against a wall. It is in static equilibrium making an angle

θ

with the horizontal floor. The coefficient of friction between the wall and the ladder is

μ_{1}

and that between the floor and the ladder is

μ_{2}

. The normal reaction of the wall on the ladder is

N_{1}

and that of the floor is

N_{2}

. If the ladder is about to slip, then

Question Image

MEDIUM

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A block of mass $m$ slides along a floor while a force of magnitude $F$ is applied to it at an angle $θ$ as shown in figure. The coefficient of kinetic friction is $μ_{K}$ . Then, the block's acceleration $a$ is given by : ( $g$ is acceleration due to gravity)

Question Image

MEDIUM

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

The following observations were taken for determining surface tension

T

of water by capillary method:

diameter of capillary,

D = 1.25 \times 10^{- 2} m

rise of water,

h = 1.45 \times 10^{- 2} m

Using

g = 9.80 m s^{- 2}

and the simplified relation

T = \frac{r h g}{2} \times 10^{3} N m^{- 1}

the possible error in surface tension is closest to:

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

When one end of the capillary is dipped in water, the height of the water column is

h

. The upward force of

105 dyne

due to surface tension is balanced by the force due to the weight of the water column. The inner circumference of the capillary is
(Surface tension of water

= 7 \times 10^{- 2} N m^{- 1})

HARD

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

Assume that a drop of a liquid evaporates by a decrease in its surface energy so that its temperature remains unchanged. The minimum radius of the drop for this to be possible is. (The surface tension is

T

, the density of the liquid is

ρ

and

L

is its latent heat of vaporisation.)

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

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

and kept in equilibrium 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:

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A body of mass

2 kg

is kept by pressing to a vertical wall by a force of

100 N

. The friction between wall and body is

0.3

. Then the frictional force is equal to

MEDIUM

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A liquid does not wet the solid surface if angle of contact is:

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A block rests on a rough inclined plane making an angle of

30 °

with the horizontal. The coefficient of static friction between the block and the plane is

0.8

. If the frictional force on the block is

10 N

, the mass of the block is

(g = 10 m s^{- 2})

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

What causes the free surface of a liquid to have minimum area?

EASY

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

Water does not wet an oily glass because

HARD

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A small box resting on one edge of the table is struck in such a way that it slides off the other edge,

1 m

away, after

2

seconds. The coefficient of kinetic friction between the box and the table

MEDIUM

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A block

A

of mass

m_{1}

rests on a horizontal table. A light string connected to it passes over a frictionless pulley at the edge of table and from its other end another block

B

of mass

m_{2}

is suspended. The coefficient of kinetic friction between the block and the table is

μ_{k}

. When the block

B

is sliding on the table, the tension in string is:

MEDIUM

Physics>Mechanics>Laws of Motion>Static and Dynamic Friction

A car is negotiating a curved road of radius

R

. The road is banked at an angle

θ

. The coefficient of friction between the tyres of the car and the road is

μ_{s}

. The maximum safe velocity on this road is:

Important Questions on Laws of Motion

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