Physics · Science General

Newtonian Mechanics and Forces

1,605 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 friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

Friction is minimised by using

  1. Wheels and balI bearings

  2. More number of tyres in a car

  3. Rough surfaces

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

Answer is A.

Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers 'bear' the load, allowing the device to spin smoothly.
The concept behind a bearing is very simple. Things roll better than they slide. The wheels on our car are like big bearings. If we had something like skis instead of wheels, our car would be a lot more difficult to push down the road.
That is because when things slide, the friction between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, the friction is greatly reduced.

Multiple choice physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

The force of friction on a static body ________ , if It is on a rough surface then.

  1. is always zero

  2. may be gravity.

  3. may be zero

  4. both B & C
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The force of friction f is always opposite the direction the object that is moving . If the object would move, then the direction of the force of friction f will be opposite the movement. If the object would not move when there is no friction, then the force of friction is zero.Hence, though the surfaces of the object are rough the force of friction can be zero if the object would not move.

Multiple choice physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

Friction depends upon ................. of surfaces.

  1. mass.

  2. nature of body.

  3. both A & B

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

Friction depends upon mass and nature of the body of surfaces.
Friction depends partly on the smoothness of the contacting surfaces, a greater force being needed to move two surfaces past one another if they are rough than if they are smooth. However, friction decreases with smoothness only to a degree; friction actually increases between two extremely smooth surfaces because of increased attractive electrostatic forces between their atoms. 
Friction does not depend on the amount of surface area in contact between the moving bodies or (within certain limits) on the relative speed of the bodies. It does, however, depend on the magnitude of the forces holding the bodies together. 
When a body is moving over a horizontal surface, it presses down against the surface with a force equal to its weight, i.e., to the pull of gravity upon it; an increase in the weight of the body causes an increase in the amount of resistance offered to the relative motion of all the surfaces in contact.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

While opening a tap with two fingers, the forces applied are  

  1. equal in magnitude

  2. parallel to each other

  3. opposite in direction

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

While opening a tap with two fingers, a couple should be applied which is defined as a pair of parallel equal forces acting in opposite direction about two different axis.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

On applying a constant torque on a body-

  1. linear velocity increases

  2. angular velocity changes

  3. it will rotate with constant angular velocity

  4. it will move with constant velocity
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A constant torque applied to a rigid body results in constant angular acceleration, which causes the angular velocity to change over time.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

It becomes easier to open or close a door turning about its hinges if the force is applied at the:

  1. Two third of the door

  2. Free edge of the door

  3. Middle of the door

  4. Point near the hinges
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Torque acting about any point O         $\tau _o = rF$                 for $sin\theta = 1$

where $r$ is the distance of the application of force from point O.
As  $r$ is maximum when a force is applied at the free end of the door, thus less amount of force is required to produce the same torque. Hence it is easier to open or close the door if force is applied at its free end. 

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

The angular momentum of body remains conserve if:

  1. applied force on body is zero

  2. applied torque on body is zero.

  3. applied force on body is constant

  4. applied torque on body is constant.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Just as linear momentum is conserved when there is no net external forces$,$

angular momentum is constant or conserved when the net torque is zero$.$
Hence,
option $(B)$ is correct answer.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

A body is acted upon by two unequal forces in opposite directions, but not in same line. The effect is that:

  1. the body will have only the rotational motion.

  2. the body will have only the translational motion.

  3. the body will have neither the rotational motion nor the translational motion.

  4. the body will have rotational as well as translational motion.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Due to unequal forces, the net force will act on the body, so the forces are unbalanced and the unbalanced forces cause a change in motion. This means body having translational motion.
There also be torque acting on the body due to unbalanced force. So there will be rotational motion too.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

A body is acted upon by two forces each of magnitude $F$, but in opposite directions. State the effect of the forces if both forces act at the same point of the body. Which of the following is/are true?

  1. Resultant force $=0$
  2. Moment of forces $=0$

  3. No motion

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

Here, we are applying two force in same magnitude but in opposite that is one is F and -F. Hence resultant force is $F + (-F) = 0 $. 

Hence, resultant force is zero. Here perpendicular distance is same for both the forces.
Hence, if we calculate $r \times F$ cross product. We get the same magnitude of moments but opposite in direction as force are of opposite in direction. Hence moments are also zeroes. Without any resultant and moment there will be no motion.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

A body is under the action of two equal and oppositely directed forces and the body is rotating with constant non-zero angular acceleration. Which of the following cannot be the separation between the lines of action of the forces?

  1. $1m$
  2. $0.4m$
  3. $0.25m$

  4. zero
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A pair of equal and opposite forces acting on a body is called a couple.

It only gives a rotating effect to the body and the torque due to a couple is
given by $\tau = Fd$
where $F$ is equal to the  magnitude of one of the forces and 
$d$ is the distance between their points of application.
To produce a non-zero angular acceleration , the torque on the body must be non zero.
Hence , the couple can give a non-zero angular acceleration to the body
only when the distance between the points of applications of the forces is non-zero.