Physics · Science General

Newtonian Mechanics and Forces

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Newtonian mechanics studies the motion of objects and the physical laws governing them. This hub covers friction, gravitational force, inertia, and vector quantities. Mastering these fundamental physics concepts is essential for various government competitive exams.

Laws of motionFriction and inertiaVector and scalar quantitiesGravitational accelerationArchimedes principle

Newtonian Mechanics and Forces Questions

Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

Which of the following equations or principle is most suitable to solve given question.  

A block of mass $m$ remains at rest on a table when a piece of paper is pulled out from under it.

  1. Newton's first law(law of inertia)
  2. Newton's second law ($F _{net}$ = ma)

  3. Newton's third law (For every action there is an equal and opposite reaction)

  4. Newton's law of universal gravitation

  5. Conservation of linear momentum
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Newton's First Law of Motion - sometimes referred to as the law of inertia states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Hence a piece of mass remains at rest on a table when a piece of paper is suddenly pulled out from under it.

Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

If no force acts on a body, then what will happen to it?

  1. It does not change its shape.

  2. It continues to move but with less speed.

  3. It changes its direction.

  4. It can either remain at rest or continue to move in a straight line.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The force is define as $F=ma$
hence acceleration is $a=\dfrac{F}{m}$
if  balanced force acts on a body F is  zero hence body must not be accelerated. hence by eq of motion $u=v=at,a=0\implies u=v$ if v=0,u=0
It can either remain at rest or continue to move in a straight line.
Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

Physical independence of force is a con-sequence of 'X'. Identify 'X'.

  1. Newton's third law of motion

  2. Newton's second law of motion

  3. Newton's first law of motion

  4. All of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Physical independence of force is a con-sequence of 'X'.

X is Newton's first law of motion Newton's first law of motion - sometimes referred to as the law of inertia. An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force

Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

When a bus suddenly takes a turn, the passengers are thrown outwards because of 

  1. Inertia of motion

  2. Acceleration of motion

  3. Speed of motion

  4. Both (b) and (c)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to law of inertia of motion a body will continue moving with constant velocity until unless any force is acting on it. When a bus is moving straight the passengers inside are also moving straight but when suddenly bus turn left passengers still continue to move straight  because no force is acting on passengers so they will move with same magnitude and direction i.e. outwards when bus turns .

Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

Newtons law are not valid in

  1. Both inertial as well as non- inertial frame of reference.

  2. A frame moving with constant velocity w.r.t. an inertial frame.

  3. All reference frames which are at rest w.r.t. an inertial frame.

  4. The reference frame attached to the earth.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Newton's Law is only valid in inertial frame of reference. If there is a non - inertial frame of reference then it won't be valid. 

Hence option $\textbf A$ is the correct answer.

Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

Statement 1 : There can be displacement of an object even in the absence of any force acting on it.
Statement 2 : An object in uniform motion in a straight line shows displacement even when the net force acting on it is zero.

  1. Both statement 1 and statement 2 are true and statement 2 is correct explanation of statement 1

  2. Both statement 1 and statement 2 are true, but statement 2 is not correct explanation of statement 1

  3. Statement 1 is true but statement 2 is false

  4. Statement 1 is false but statement 2 is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

If any body is in the state of rest or in uniform motion, it remains in that state until an external force is applied on it. 
So, if a body is initially moving with some constant velocity, it can continue to move with same velocity even if no external force is acting on it.
In fact, the effect of force is to accelerate and not just displace. For example, an object moving straight in space far away from any celestial objects will continue to move forever, although there is no force acting on it. This is due to Newton's first law of motion or law of inertia.
Hence, Both statement 1 and statement 2 are true and statement 2 is correct explanation of statement 1.

Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

While dusting a carpet, we give it a sudden jerk or beat it with a stick because: 

  1. the inertia of rest keeps the dust in its position and the dust is removed when the carpet moves away.

  2. the inertia of motion removes dust.

  3. no inertia involved in process.

  4. jerk compensates for the force of adhesion between dust and carpet and dust is removed.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

While dusting we give a sudden serk our beat with stick because when we do that stick because when we do that the particle of carpet move with our help and the dust particle stays at rest by inertia and eventually they separate from the carpet.

Multiple choice physics force and newton's laws of motion first law of motion newton's first law of motion momentum and newton's laws

Inertia is the property of a body which preserves its state of motion or uniform motion in a straight line. The following factors tell me about inertia.
I. Greater the mass of a body, greater is its inertia.
II. Greater the inertia of a body, the less will be the acceleration produced by a given force.
III. The law of inertia is the same as Newton's first law of motion. 
Which combination is true?

  1. I and III only

  2. I and II only

  3. I, II and III

  4. II and III only
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

All three statements are standard definitions and properties related to inertia and Newton's first law of motion.

Multiple choice physics types of energy renewable and non-renewable resources renewable and non-renewable sources of energy substances, objects and energy

A body is falling freely under the action of gravity alone in vacuum. Which of the following quantities remain constant during the fall?

  1. Kinetic energy

  2. Potential energy

  3. Total mechanical energy

  4. Total linear momentum
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
As the body is falling freely under gravity, the potential energy decreases continuously and kinetic energy increases continuously as all the conservative forces are doing work. So, total mechanical energy $(PE + KE)$ of the body will be constant.
At point A total mechanical energy will be $EA = K.E + P.E$
$E _{A}=\dfrac{1}{2}mv^{2}+m _{g}H$
As velocity will be zero at $A$, so its kinetic energy will be zero 
$E _{A}=M _{g}H$
Velocity at point $B$ will be 
$V _{B}=\sqrt{2gh}$
So energy at point $B$ will be 
$E _{B}=KE+PE$
$E _{B}=\dfrac{1}{2}m(2gh)+mg(H-h)$
$E _{B}=mgh+mgH-mgh$
$E _{B}=mgH$
Now velocity at point $C$ will be 
$V _{C}=\sqrt{2gh}$
So energy at point $C$ will be
$ E _{C}=KE+PE$
$E _{C}=\dfrac{1}{2}m(2gH)+mg(0)$
So, total mechanical energy will remain same (if we neglect the air friction).
Multiple choice physics types of energy renewable and non-renewable resources renewable and non-renewable sources of energy substances, objects and energy

While falling

  1. Potential energy

  2. Kinetic energy

  3. Both A & B

  4. None
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

While it is falling it has certain velocity,as kinetic energy is defined as the virtue of its state of motion it will have kinetic energy.As it is at certain height it will have Potential energy which is defined by virtue of state of its position.Hence ball has both potential and kinetic energy.