Laws of Motion Test

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Laws of Motion Test - 22

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Question 1
1 / -0

A metallic ball strikes a wall and falls down whereas a tennis ball having the same mass and velocity bounces back. The conclusion from this is that :

A
Both suffer equal change in momentum

B
The tennis ball suffers a greater change in momentum

C
Metallic ball suffers a greater change in momentum

D
The momentum of the tennis ball is less than that of the metallic ball

Solution

For metallic ball,
$$ \triangle P_M =0-mu=-mu$$
For tennis ball,
$$ \triangle P_T= -mu-mu = -2mu$$
$$ \therefore Option\ B\ is\ correct.$$
Question 2
1 / -0

Impulse is

A
a scalar quantity

B
a vector quantity

C
neither a scalar nor a vector

D
sometimes a scalar and sometimes a vector

Solution

Explanation:
$$\bullet$$Impulse is change in momentum. So, it is a difference between the final momentum and initial momentum.
$$\bullet$$Momentum is vector quantity that has both magnitude and direction. So, the impulse will also have both magnitude and direction. So, impulse is vector quantity.

$$Answer:$$

Hence, option B is the correct answer.
Question 3
1 / -0

Choose the wrong statement:

A
1 kg wt = 9.8 N

B
Momentum is a vector quantity.

C
Force is always conserved.

D
Momentum is conserved in the absence of an external force.

Solution

$$ 1kg-wt = 1 \times 9.8 N $$
$$ momentum = mass \times velocity $$ As velocity is vector, momentum is vector.
Friction is non conservative force.
According to Newton's second law, rate of change of momentum is directly proportional to applied force.
So,if force is zero, momentum is conserved.
So wrong statement is option C.
Question 4
1 / -0

Every action has reaction. These action-reaction are

A
Equal, opposite and acting on the same body

B
Equal, in the same direction and acting on same body

C
Equal, opposite and acting on different bodies

D
Equal, in same direction and acting on different bodies.

Solution

According to Newton third law
The forces of action and reaction are equal, opposite and act on different bodies.
The effect of action and reaction is always visible separately on both the interacting bodies in opposite directions. Therefore, the forces of action and reaction are equal, opposite and act on different bodies.
Question 5
1 / -0

A body of mass M collides with a wall with velocity V and rebounds with the same speed. Its change in momentum is equal to :

A
Zero

B
MV

C
2MV

D
3MV

Solution

$$\Delta P={ P }_{ 1 }-{ P }_{ 2 }$$ $$[$$ change in momentum$$]$$
$$=MV-(-MV)\\ \quad \quad \quad =-2MV$$
negative sign denotes direction.
Hence option C is correct.
Question 6
1 / -0

When a body is in translatory equilibrium

A
The body is definitely at rest

B
The body is definitely in the state of uniform motion

C
The body will be either at rest or in the state or uniform motion

D
None of these

Solution

When a body is in translatory equilibrium , the net force acting on a body is zero, and the body is said to be in translational equilibrium. In translatory equilibrium, the center of mass of the body remains either at rest or moves rectilinearly with constant velocity. Hence, the body is definitely in the state of uniform motion or in rest.
Question 7
1 / -0

A ball of mass $$\dfrac{1}{10}$$ kg is thrown against a wall. It strikes the wall normally with a velocity of $$\displaystyle 30{ ms }^{ -1 }$$ and rebounds from there with a velocity $$\displaystyle 20{ ms }^{ -1 }$$. The impulse of the force exerted by the ball on the wall is

A
0.5Ns

B
50Ns

C
5 Ns

D
1Ns

Solution

Impulse = force x time
= change in momentum
$$= mv - mu =0.1(-20-30) =-5$$

Since units in all the options are same, we need not bother to think about the units. Also since there is no fight of plus or minus sign in the options, we will give the correct answer as 5 Ns. Note that the direction of initial velocity is considered as positive and that of the final velocity is considered as negative
Question 8
1 / -0

A long-jumper runs before jumping to

A
Cover greater distance

B
Maintain momentum conservation

C
Gain energy by running

D
Gain momentum

Solution

While running a long distance, jumper tries to gain more velocity that increases his momentum. When he jumps, due this momentum, his body covers longer distance.
So, Option D is correct.
Question 9
1 / -0

A cannon after firing recoils due to

A
Conservation of energy

B
Backward thrust of gases produced

C
Newton's first law of motion

D
Newton's third law of motion

Solution

Correct Option is D.
Explanation for the correct:
$$\bullet$$ Newton's Third Law of Motion states that to every Action there is equal and opposite Reaction. Thus firing of bullet from cannon is an Action and there is opposite Reaction on the cannon due to which it recoils. Option D is correct.
$$\bullet$$ Conservation of Energy states that Energy can neither be created nor destroyed. It can only change it forms.
$$\bullet$$ Backward thrust of gases is not a Law. It is also one of the consequences of Third Law of Motion.
$$\bullet$$ First Law of Motion states that if a body is at rest/motion it will continue to remain at rest/motion until any external force is applied.

Thus, Only Option D is correct.
Question 10
1 / -0

Choose the wrong statement

A
$$1 kg \ wt = 9.8 N$$

B
Momentum is a vector quantity

C
Force is always conserved

D
Momentum is conserved in the absence of an external force

Solution

Forces that do not store energy are called nonconservative or dissipative forces. Friction is a nonconservative force, and there are others. Any friction-type force, like air resistance, is a nonconservative force.
Force is always conserved is the wrong statement.

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Laws of Motion Test - 22

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Laws of Motion Test - 22

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Question 1

Both suffer equal change in momentum

The tennis ball suffers a greater change in momentum

Metallic ball suffers a greater change in momentum

The momentum of the tennis ball is less than that of the metallic ball

Solution

Question 2

a scalar quantity

a vector quantity

neither a scalar nor a vector

sometimes a scalar and sometimes a vector

Solution

Question 3

1 kg wt = 9.8 N

Momentum is a vector quantity.

Force is always conserved.

Momentum is conserved in the absence of an external force.

Solution

Question 4

Equal, opposite and acting on the same body

Equal, in the same direction and acting on same body

Equal, opposite and acting on different bodies

Equal, in same direction and acting on different bodies.

Solution

Question 5

Zero

MV

2MV

3MV

Solution

Question 6

The body is definitely at rest

The body is definitely in the state of uniform motion

The body will be either at rest or in the state or uniform motion

None of these

Solution

Question 7

0.5Ns

50Ns

5 Ns

1Ns

Solution

Question 8

Cover greater distance

Maintain momentum conservation

Gain energy by running

Gain momentum

Solution

Question 9

Conservation of energy

Backward thrust of gases produced

Newton's first law of motion

Newton's third law of motion

Solution

Question 10

$$1 kg \ wt = 9.8 N$$

Momentum is a vector quantity

Force is always conserved

Momentum is conserved in the absence of an external force

Solution

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