Forces and Laws of Motion Test

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Forces and Laws of Motion Test - 15

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Weekly Quiz Competition

Question 1
1 / -0

A machine gun fires a bullet of mass $$40 \ g$$ with a velocity $$1200 \ ms^{-1}$$. The man holding it can exert a maximum force of $$144 \ N$$ on the gun. How many bullets can he fire per second at the most?

A
$$One$$

B
$$Four$$

C
$$Two$$

D
$$Three$$

Solution

Mass of the bullet $$m=40 \ g=0.040 \ kg$$
Velocity with which the bullet leaves the gun $$v=1200 \ ms^{-1}$$

We know that
Force $$F=\dfrac{\Delta P}{\Delta t}$$
$$\implies \Delta P=F. \Delta t$$ . . . (i)

Change in momentum for each bullet $$\Delta p=p_f-p_i=mv-0=mv$$
Let there be $$n$$ bullets fired per second.
So total mass of bullets fired per sec $$M=n \times m$$
Total change in momentum for one second $$\Delta P=Mv=(n \times m)v . . . (ii) =mnv$$

Now,
Force exerted by man: $$F=144 N$$
Time interval to accomplish the change in momentum $$\Delta t = 1 \ sec$$

Using (i) and (ii),
$$F. \Delta t=mnv$$
$$\Rightarrow 144 \times 1=n(0.040)(1200)$$
So, number of bullets fired per second
$$n=\dfrac{144}{0.040 \times 1200} = 3$$

Option D is the answer.
Question 2
1 / -0

Cleaning of dust from carpet is due to _____.

A
Inertia of motion

B
Inertia of rest

C
Inertia of direction

D
Momentum

Solution

Cleaning of dust from the carpet is due to the inertia of rest that the particle tends to remain at rest if no external force is applied to it.
When we beat a carpet with the help of a stick, the carpet comes into a motion whereas the dust particle remain at rest due to their inertia of rest and hence get separated out of the carpet.
Question 3
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Assertion (A): According to Newton’s third law sum of action and reaction is not equal to zero
Reason (R) : The forces action and reaction acts on different bodies.

A
A and R are correct and R is the correct explanation of A

B
A and R are correct and R is not the correct explanation A

C
A is true and R is false

D
A is false and R is true

Solution

option D is correct .the action and reaction forces are equal in magnitude and opposite in direction. therefore their sum is zero
they act on different bodies
Question 4
1 / -0

A force of 12 N gives an object an acceleration of 4m/s$$^{2}$$. The force required to give it an acceleration of 10m/s$$^{2}$$ is

A
15 N

B
20 N

C
25 N

D
30 N

Solution

The force $$F=ma$$.
Using this, the mass of the object will be $$m=12/4 =3Kg$$.
So, the force required to give it an acceleration of $$10 m/s^2$$ is $$30N$$.
Question 5
1 / -0

If action force acting on a body is gravitational in nature, the reaction force:

A
may be a contact force

B
must be gravitational too

C
may be a gravitational or contact force

D
may be a force of any origin

Solution

By Newton's third law, every action has an equal and opposite reaction.
Therefore, if a force acting on a body is gravitational in nature, the same must be true for the reaction force which acts as an action force on other body.

Question 6

1 / -0

Match list (I) with List (II)

List I	List II
a) Recoil of gun	e) Newtons first law
b) Acceleration in one dimension and motion in two dimensions	f) Newtons second law
c) Definition of force	g) Projectile motion
d) Measurement of force	h) Newton’s third law

$$a\rightarrow e, b\rightarrow g,c\rightarrow h, d\rightarrow f.$$

$$a\rightarrow h, b\rightarrow g,c\rightarrow e, d\rightarrow f.$$

$$a\rightarrow e, b\rightarrow h,c\rightarrow g, d\rightarrow f.$$

$$a\rightarrow h, b\rightarrow e,c\rightarrow g, d\rightarrow f.$$

Solution

Recoil is caused due to the force exerted by the bullet on the gun which in turn is felt by the hand i.e. the force exerted by the gun on the bullet and that by the bullet on the gun form an action-reaction pair and follow Newton's 3rd law.
In projectile motion, the body has acceleration only in the y-direction but there is motion in both x and y-directions.
Definition of force comes from the Newton's 1st law which defines force as the physical quantity responsible for changing the state of motion of a body.
Newton's 2nd law of motion quantifies force as the rate of change of momentum pet unit time. By this we get,

$$\vec{F}=\dfrac{d\vec{P}}{dt}=m\dfrac{d\vec{v}}{dt}=ma$$

Question 7
1 / -0

Which of following Newton's laws reveals the underlying symmetry in the forces that occur in nature?

A
First law

B
Second law

C
Third law

D
Law of gravitation

Solution

Newton's third law of motion states that all the forces in nature have an equal and opposite reaction force present. This explains the underlying symmetry in the forces that occur in nature.
Question 8
1 / -0

Which of the following is the most significant law of motion given by Newton?

A
First law of motion

B
Second law of motion

C
Third law of motion

D
Zeroth law of motion

Solution

Newton's second law of motion states that the force on a body is equal to the rate of change of momentum of the body and its direction is the same as that of the change in momentum. Alternatively, this law defines force as mass times acceleration, i.e. $$F=m\times a.$$

Since this law gives a quantitative definition of force, it is the most significant law of motion out of the three. The other two laws can be explained using the second law of motion.
Question 9
1 / -0

A man is stranded in the middle of a perfectly smooth island of ice, where there is no friction between the ground and his feet. Under these circumstances,

A
he can reach the desired corner by throwing any object in the same direction

B
he can reach the desired corner by throwing any object in the opposite direction

C
he has no chance of reaching any corner of the island

D
he can reach the desired corner by walking on the ground in that direction

Solution

Since the surface is frictionless, there would be no external force and hence no external impulse. Hence, linear momentum would be conserved. So if he throws an object in a particular direction, he would get an impulse in the opposite direction and would acquire a constant velocity.
Question 10
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Action and reaction forces never balance out. Because,

A
they are equal but not opposite always

B
they are unequal in magnitude even though opposite in direction

C
they act on different bodies

D
they are unequal in magnitudes

Solution

Action and reaction exist in pair and are always equal in magnitude and opposite in direction. But they act on different bodies, hence they cannot balance each other.

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Forces and Laws of Motion Test - 15

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Question 1

$$One$$

$$Four$$

$$Two$$

$$Three$$

Solution

Question 2

Inertia of motion

Inertia of rest

Inertia of direction

Momentum

Solution

Question 3

A and R are correct and R is the correct explanation of A

A and R are correct and R is not the correct explanation A

A is true and R is false

A is false and R is true

Solution

Question 4

15 N

20 N

25 N

30 N

Solution

Question 5

may be a contact force

must be gravitational too

may be a gravitational or contact force

may be a force of any origin

Solution

Question 6

$$a\rightarrow e, b\rightarrow g,c\rightarrow h, d\rightarrow f.$$

$$a\rightarrow h, b\rightarrow g,c\rightarrow e, d\rightarrow f.$$

$$a\rightarrow e, b\rightarrow h,c\rightarrow g, d\rightarrow f.$$

$$a\rightarrow h, b\rightarrow e,c\rightarrow g, d\rightarrow f.$$

Solution

Question 7

First law

Second law

Third law

Law of gravitation

Solution

Question 8

First law of motion

Second law of motion

Third law of motion

Zeroth law of motion

Solution

Question 9

he can reach the desired corner by throwing any object in the same direction

he can reach the desired corner by throwing any object in the opposite direction

he has no chance of reaching any corner of the island

he can reach the desired corner by walking on the ground in that direction

Solution

Question 10

they are equal but not opposite always

they are unequal in magnitude even though opposite in direction

they act on different bodies

they are unequal in magnitudes

Solution

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