Physics · Science General

Newtonian Mechanics and Forces

1,559 Questions

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 turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

One can lean further to one side or the other without creating enough turning force to tip him over. This is because 

  1. The person has low centre of gravity

  2. The person has no centre of gravity

  3. The person has high centre of gravity

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Center of gravity is the point at which the entire weight of a body may be considered as concentrated so that if supported at this point the body would remain in equilibrium.

One can lean further to one side or other without creating enough turning force to tip him over. This is because the person has low center of gravity as having a low center of gravity decreases the torque hence the person will not tip over.

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

What is the center of gravity of an object?

  1. The point where gravity appears to act.

  2. The point where gravity doesn't act.

  3. The point where the force of gravity is strongest.

  4. The point where the force of gravity is weakest.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Option A is the definition of the centre of gravity. B is a contradiction. As far as C ad D are concerned, the force of gravity is equal at all points provided the object is small as compared to the radius of the planet. 

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

Which one of following statements related to center of gravity is incorrect?

  1. The center of gravity of an object is defined as point through which its whole weight appears to act.

  2. The center of gravity is sometimes confused with center of mass.

  3. The center of gravity always lies inside object.

  4. For an object placed in a uniform gravitational field, center of gravity coincides with center of mass.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

A is the proper definition. In some bodies like hollow bodies, frames and rings, the center of gravity is at the geometric centre where the matter of the object is not present.

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

The stability of a flexible body depends on:

  1. height of the center of gravity from the ground.

  2. base area of the body.

  3. shape of the body.

  4. all the above.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The stability of objects depends on the base, C.G and shape of the body. For a body to be the stable,

  1. The base of the body need to be broad.
  2. The Centre of gravity should be as low as possible.
  3. The vertical line through the center of gravity should fall within the base.

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

People can spin a ball on their finger. This is due to

  1. the centre of gravity of the ball is on his finger.

  2. the resultant force is passing through the centre of gravity of the ball.

  3. the resultant force is passing through the centre of the ball.

  4. both A and B
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

let us assume body of mass m and divide it into many small particles. The centre of mass means it is the mean value of the all the small particles . it would more clear by assuming the body in 3-D coordinate system and calculate its mean of all small particles with the co ordinates in three dimension . where as the centre of gravity is also same but it is the mean of its weight. it is the point were total weight acts


we may think  both be same but not always. because in above example the value of g will be different at different positions because of that while calculating the mean the centre will shifts from centre of mass


in the question given the centre of mass will be exact center of ball and centre of gravity also lies at the center of mass as the ball is small there will be no greater effect by g. so the the centre of gravity of ball is on finger and resultant force is weight which is all acts on center of ball

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

If we suspend lamina at different positions, its center of gravity will still lie along the :

  1. plumb line

  2. line of force

  3. line of weight

  4. gravity line
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

let us assume body of mass m and divide it into many small particles. The centre of mass means it is the mean value of the all the small particles . it would more clear by assuming the body in 3-D coordinate system and calculate its mean of all small particles with the co ordinates in three dimension . where as the centre of gravity is also same but it is the mean of its weight. it is the point were total weight acts

we may think  both be same but not always. because in above example the value of g will be different at different positions because of that while calculating the mean the centre will shifts from centre of mass 
  because  suspension of the body at the different position the value of g value effects at some point so the centre of gravity will shifts but stays along blub line



Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity
Around the centre of gravity ______ vanishes. Fill in the blank. 

  1. Resultant acceleration due to gravity force

  2. Resultant velocity due to gravity force

  3. Resultant torque due to gravity force

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

Resultant torque due to gravity force vanishes around the centre of gravity because perpendicular distance between the gravitational force and the point about that toque is calculated becomes very very small or almost zero.

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

An object will not undergo rotational motion when:

  1. the forces are acting on it at different positions

  2. every forces is creating different turning effects

  3. every moment has the same amplitude

  4. all the forces are acting at its centre of gravity
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For an object to undergo rotational motion, a net torque must be exerted on the object. If all the forces are acting at its centre of gravity, net torque acting on the object is zero and so the object will not undergo any rotational motion.

Multiple choice physics turning effects of forces centre of gravity forces - vectors and moments acceleration due to gravity

An object after deforming 

  1. may have different centre of mass.

  2. have same centre of mass

  3. doesn't change its centre of gravity

  4. none of the above

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Centre of mass is a point on a physical body which behaves as if the whole mass is concentrated over there. Whenever a force acts on a body it appears to be acting on the centre of mass. 

The centre of mass depends upon how the particles of the body are scattered around it. It is closer towards the heavier regions of the body as compared to the lighter regions.  Whenever an object is deformed, its heavier regions may change their locations. As a result, the centre of mass may change its location

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

Mark the correct option

  1. The state of motion of an object is described by its speed only

  2. Many a time application of force does not result in a change in the state of motion of an object

  3. By sitting on a bicycle seat force is applied to the spring fixed to the seat of a bicycle

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
$(i)$ option $A$ is correct, as if to know about the unifomity of a motion and the body is moving or not speed is used as the parameter
$(ii)$Option B is correct, as the acceleration of a body depends on the net force a applied not on single $10r$ individual forces.
$(iii)$ Option $C$ is correct, while sifting on the bicycle, the spring force allached to the seat balances weight.
Option $D$ 

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

Consider the following statements
I) When a body is travelling with uniform speed, no force is acting on it.
II) When a body is travelling with constant velocity, no force is acting on it.
Which of the above statements is/are true?

  1. only I

  2. only II

  3. both I and II

  4. neither I nor II
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to Newton's first law, a body moving with a constant velocity has zero acceleration and therefore experiences no net external force. Uniform speed only specifies the magnitude of velocity, meaning direction could change, which would require a centripetal force. Thus, only statement II correctly implies zero net 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

Newton's law of motion cannot be applicable to the particle moving at a speed comparable to the speed of

  1. $Light$
  2. $Sound$
  3. $Rocket$
  4. $Bullet train$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Newton's law of motion are applicable for matter which occupy some space and have some mass. It is not possible for any matter to travel with speed of light. Secondly the mass charges as the speed approaches speed of light. Newton's law is applicable only when mass is constant so light is correct option.

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

Choose the correct statement(s)

  1. Motion necessarily takes place along the direction of force

  2. If no force acts, the body is at rest

  3. A body in motion, need not be acted upon by a force

  4. A change in speed is always there, whenever a force is applied on the moving body
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Motion always takes place along velocity of the body.So it does not necessarily takes place along the direction of force.
When a body moves with uniform velocity , there is no force acting on the body. So option B is incorrect and C is correct.
We know that magnetic force does not do work. It can change the direction of motion but never change the speed. So option D is incorrect.