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Assertion: A lighter and a heavier bodies moving with same moment and experiencing same retarding force have equal stopping times.

Reason: For a given force and momentum, stopping time is independent of mass.

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Important Questions on Laws of Motion

EASY

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

A block kept on a rough inclined plane, as shown in the figure, remains at rest upto a maximum force

2 N

down the inclined plane. The maximum external force up the inclined plane that does not move the block is

10 N .

The coefficient of static friction between the block and the plane is: [Take

g = 10 m s^{- 2}

]

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

What is the minimum velocity with which a body of mass m must enter a vertical loop of radius

R

so that it can complete the loop?

EASY

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

A curved road of diameter

1.8 km

is banked so that no friction is required at a speed of

30 m s^{- 1}

. What is the banking angle?

EASY

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

Which of the following is a self adjusting force?

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:

HARD

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

A particle is moving in a circular path of radius a under the action of an attractive potential

U = - \frac{k}{2 r^{2}} .

Its total energy is:

HARD

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

A given object takes

n

times more time to slide down a

45^{o}

rough inclined plane as it takes to slide down a perfectly smooth

45^{o}

incline. The coefficient of kinetic friction between the object and the incline is:

MEDIUM

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

The coefficient of friction between two surfaces is

μ = 0.8

. The tension in the string shown in the figure is -
Question Image

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 :

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

is placed on a surface with a vertical cross section given by

y = \frac{x^{3}}{6}

. If the coefficient of friction is

0.5

, the maximum height above the ground at which the block can be placed without slipping is

MEDIUM

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

A plank with a box on it at one end is gradually raised about the other end. As the angle of inclination with the horizontal reaches

30 °

, the box starts to slip and slides

4.0 m

down the plank in

4.0 s

. The coefficients of static and kinetic friction between the box and the plank will be, respectively:
Question Image

MEDIUM

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

A heavy box is to be dragged along a rough horizontal floor. To do so, the person

A

pushes it at an angle

30 °

from the horizontal and requires a minimum force

F_{A}

, while the person

B

pulls the box at an angle

60 °

from the horizontal and needs minimum force

F_{B}

. If the coefficient of friction between the box and the floor is

\frac{\sqrt{3}}{5}

, the ratio

\frac{F_{A}}{F_{B}}

HARD

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

A system consists of three masses

m_{1}, m_{2}

and

m_{3}

connected by a string passing over a pulley

P .

The mass

m_{3}

hangs freely and

m_{2}

and

m_{1}

are on a rough horizontal table (the coefficient of friction

= μ) .

The pulley is frictionless and of negligible mass. The downward acceleration of mass

m_{3}

is: (Assume

m_{1} = m_{2} = m_{3} = m)

HARD

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

A point particle of mass m, moves along the uniformly rough track PQR as shown in the figure. The coefficient of friction, between the particle and the rough track equals

μ

. The particle is released, from rest, from the point P and it comes to rest at a point R. The energies, lost by the ball, over the parts, PQ and QR, of the track, are equal to each other, and no energy is lost when particle changes direction from PQ to QR.
The values of the coefficient of friction

μ

and the distance

x = (Q R)

, are respectively close to:

Question Image

MEDIUM

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

A block of mass

10 kg

is kept on a rough inclined plane as shown in the figure. A force of

3 N

is applied on the block. The coefficient of static friction between the plane and the block is

0.6 .

What should be the minimum value of force

P,

such that the block does not move downward? (take

g = 10 m s^{- 2}

)

EASY

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

Which one of the following statements is incorrect?

MEDIUM

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

The potential energy of a particle of mass m at a distance r from a fixed point O is given by

V (r) = k r^{2} / 2

, where k is a positive constant of appropriate dimensions. This particle is moving in a circular orbit of radius R about the point O. If v is the speed of the particle and L is the magnitude of its angular momentum about O, which of the following statements is (are) true?

Assertion: A lighter and a heavier bodies moving with same moment and experiencing same retarding force have equal stopping times. Reason: For a given force and momentum, stopping time is independent of mass.

Important Questions on Laws of Motion

Learn and Prepare for any exam you want !

Assertion: A lighter and a heavier bodies moving with same moment and experiencing same retarding force have equal stopping times.

Reason: For a given force and momentum, stopping time is independent of mass.