NEWTON LAWS OF MOTION
Read the assertion and reason carefully to mark the
correct option out of the options given below:
(a) If both assertion and reason
are true and the reason is the correct explanation of the assertion.
(b) If both assertion and reason
are true but reason is not the correct explanation of the assertion.
(c) If assertion is true but
reason is false.
(d) If the assertion and reason
both are false.
(e) If assertion is false but
reason is true.
1.
Assertion : Inertia is the property by virtue of which the
body is unable to change by itself the state of rest only.
Reason : The
bodies do not change their state unless acted upon by an unbalanced external
force.
2.
Assertion : If the net external force on the body is zero,
then its acceleration is zero.
Reason : Acceleration does not depend on force.
3.
Assertion : Newton’s second law of motion gives the
measurement of force.
Reason : According
to Newton’s second law of motion, force is directly proportional to the rate of
change of momentum.
4.
Assertion : Force is required to move a body uniformly
along a circle.
Reason : When the
motion is uniform, acceleration is zero.
5.
Assertion : If two objects of different masses have same
momentum, the lighter body possess greater velocity.
Reason : For
all bodies momentum always remains same.
6.
Assertion : Aeroplanes always fly at low altitudes.
Reason : According to Newton’s third law of motion, for
every action there is an equal and opposite reaction.
7.
Assertion : No force is required by the body to remain in
any state.
Reason : In
uniform linear motion, acceleration has a finite value.
8.
Assertion : Mass is a measure of inertia of the body in
linear motion.
Reason : Greater the mass, greater is the force
required to change its state of rest or of uniform motion.
9.
Assertion : The slope of momentum versus time curve give us
the acceleration.
Reason : Acceleration is given by
the rate of change of momentum.
10.
Assertion : A cyclist always bends inwards while
negotiating a curve.
Reason : By bending,
cyclist lowers his centre of gravity.
11.
Assertion : The work done in bringing a body down from the
top to the base along a frictionless incline plane is the same as the work done
in bringing it down the vertical side.
Reason : The
gravitational force on the body along the inclined plane is the same as that
along the vertical side.
12.
Assertion : Linear momentum of a body changes even when it
is moving uniformly in a circle.
Reason : Force required to move a body uniformly along
a straight line is zero.
13.
Assertion : A bullet is fired from a rifle. If the rifle
recoils freely, the kinetic energy of rifle is more than that of the bullet.
Reason : In
the case of rifle bullet system the law of conservation of momentum violates.
14.
Assertion : A rocket works on the principle of conservation
of linear momentum.
Reason : Whenever there is a change in momentum of one
body, the same change occurs in the momentum of the second body of the same
system but in the opposite direction.
15.
Assertion : The apparent weight of a body in an elevator
moving with some downward acceleration is less than the actual weight of body.
Reason : The
part of the weight is spent in producing downward acceleration, when body is in
elevator.
16.
Assertion : When the lift moves with uniform velocity the
man in the lift will feel weightlessness.
Reason : In downward accelerated motion of lift,
apparent weight of a body decreases.
17.
Assertion : In the case of free fall of the lift, the man
will feel weightlessness.
Reason : In
free fall, acceleration of lift is equal to acceleration due to gravity.
18.
Assertion : A player lowers his hands while catching a
cricket ball and suffers less reaction force.
Reason : The
time of catch increases when cricketer lowers its hand while catching a ball.
19.
Assertion : The acceleration produced by a force in the
motion of a body depends only upon its mass.
Reason : Larger is the mass of the body, lesser will be
the acceleration produced.
20.
Assertion : Linear momentum of a body changes even when it
is moving uniformly in a circle.
Reason : In
uniform circular motion velocity remain constant.
21.
Assertion : Newton’s third law of motion is applicable only
when bodies are in motion.
Reason : Newton’s third law applies to all types of
forces, e.g. gravitational, electric
or magnetic forces etc.
22.
Assertion : A reference frame attached to earth is an
inertial frame of reference.
Reason : The
reference frame which has zero acceleration is called a non inertial frame of
reference.
23.
Assertion : A table cloth can be pulled from a table
without dislodging the dishes.
Reason : To every action there is an equal and opposite
reaction.
24.
Assertion : A body subjected to three concurrent forces cannot
be in equilibrium.
Reason : If
large number of concurrent forces acting on the same point, then the point will
be in equilibrium, if sum of all the forces is equal to zero.
25.
Assertion : Impulse and
momentum have different dimensions.
Reason : From Newton’s second law of motion, impulse is
equal to change in momentum.
ANSWERS
|
1 |
e |
2 |
c |
3 |
a |
4 |
b |
5 |
c |
|
6 |
a |
7 |
c |
8 |
a |
9 |
d |
10 |
c |
|
11 |
c |
12 |
b |
13 |
d |
14 |
a |
15 |
c |
|
16 |
e |
17 |
a |
18 |
a |
19 |
b |
20 |
c |
|
21 |
e |
22 |
d |
23 |
b |
24 |
e |
25 |
e |
1.
(e) Inertia is the property by virtue of which the
body is unable to change by itself not only the state of rest, but also the
state of motion.
2.
(c) According to Newton’s second law
Acceleration = 
i.e. if net external force on the body is zero then acceleration
will be zero
3.
(a) According to second law 
If we know the values of m and a, the force acting on the body can be calculated and hence second law gives that how much force is applied on the body.
4.
(b) When a body is moving in a circle, its speed
remains same but velocity changes due to change in the direction of motion of
body. According to first law of motion, force is required to change the state
of a body. As in circular motion the direction of velocity of body is changing
so the acceleration cannot be zero. But for a uniform motion acceleration is
zero (for rectilinear motion).
5.
(c) According to definition of momentum
if P = constant
then 
= constant or 
As velocity is inversely proportional to mass,
therefore lighter body possess greater velocity.
6.
(a) The wings of the aeroplane pushes the external
air backward and the aeroplane move forward by reaction of pushed air. At low
altitudes. density of air is high and so the aeroplane gets sufficient force to
move forward.
7.
(c) Force is required to change the state of the
body. In uniform motion body moves with constant speed so acceleration should
be zero.
8. (a) According
to Newton’s second law of motion 
i.e. magnitude of the acceleration produced by a given force is
inversely proportional to the mass of the body. Higher is the mass of the body,
lesser will be the acceleration produced i.e.
mass of the body is a measure of the opposition offered by the body to change a
state, when the force is applied i.e.
mass of a body is the measure of its inertia.
9.
(d) 
Slope of momentum-time graph
i.e. Rate of change of momentum = Slope of momentum-
time graph = force.
10. (c) The purpose of bending is to acquire centripetal force for circular motion. By doing so component of normal reaction will counter balance the centrifugal force.
11.
(c) Work done in moving an object against
gravitational force (conservative force) depends only on the initial and final
position of the object, not upon the path taken. But gravitational force on the
body along the inclined plane is not same as that along the vertical and it
varies with the angle of inclination.
12.
(b) In uniform
circular motion of a body the speed remains constant but velocity changes as
direction of motion changes.
As
linear momentum = mass × velocity, therefore linear momentum of a body changes
in a circle.
On the other hand, if the body is moving
uniformly along a straight line then its velocity remains constant and hence
acceleration is equal to zero. So force is equal to zero.
13.
(d) Law of conservation of linear momentum is
correct when no external force acts . When bullet is fired from a rifle then
both should possess equal momentum but different kinetic energy. E 
Kinetic energy of the
rifle is less than that of bullet because 
14.
(a) As the fuel in rocket undergoes combustion, the
gases so produced leave the body of the rocket with large velocity and give
upthrust to the rocket. If we assume that the fuel is burnt at a constant rate,
then the rate of change of momentum of the rocket will be constant. As more and
more fuel gets burnt, the mass of the rocket goes on decreasing and it leads to
increase of the velocity of rocket more and more rapidly.
15.
(c) The apparent
weight of a body in an elevator moving with downward acceleration a is given by 
16.
(e) For uniform motion apparent weight = Actual
weight
For downward accelerated motion,
Apparent weight < Actual weight
17.
(a)
18.
(a) By lowering his hand player increases the time
of catch, by doing so he experience less force on his hand because 
.
19.
(b) According to Newton’s second law,
For constant F,
acceleration is inversely proportional to mass i.e. acceleration produced by a force depends only upon the mass of
the body and for larger mass acceleration will be less.
20.
(c) In uniform circular motion, the direction of
motion changes, therefore velocity changes.
As P = mv therefore momentum of a body also
changes in uniform circular motion.
21.
(e) According to third law of motion it is
impossible to have a single force out of mutual interaction between two bodies,
whether they are moving or at rest. While, Newton’s third law is applicable for
all types of forces.
22.
(d) An inertial frame of reference is one which has
zero acceleration and in which law of inertia hold good i.e. Newton’s law of
motion are applicable equally. Since earth is revolving around the sun and
earth is rotating about its own axis also, the forces are acting on the earth
and hence there will be acceleration of earth due to these factors. That is why
earth cannot be taken as inertial frame of reference.
23.
(b) According to law of inertia (Newton’s first
law), when cloth is pulled from a table, the cloth come in state of motion but
dishes remains stationary due to inertia. Therefore when we pull the cloth from
table the dishes remains stationary.
24.
(e) A body subjected to three concurrent forces is
found to in equilibrium if sum of these force is equal to zero.
i.e. 
25. (e) From
Newton's second law
Impulse
= Change of momentum.
So they have equal dimensions
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