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 newton's laws of motion weightlessness application of newton's law of motion escape velocity

A 50.0 kg boy is sitting on an amusement park ride where he accelerates straight upward from rest to a speed 30.0 m/s in 3.0 s. What is his mass as he accelerates upward?

  1. 990.0 kg

  2. 100.0 kg

  3. 50.0 kg

  4. 5.00 kg

  5. 0 kg
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Mass of an object always remains constant whether the object is accelerating or not. Apparent weight of the object changes due to acceleration.

Hence the mass of the boy is $50$ kg even he accelerates upward.
Thus option C is correct.

Multiple choice physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

A plumb bob is hung from the ceiling of a train compartment. the train moves on an inclined track of inclination $30^\circ $ with horizntal. The acceleration of train up the plane is $a=\,g/2$. The angle which the string supporting the bob makes with normal to the ceiling in equilibrium is-

  1. $30^\circ $
  2. ${\tan ^{ - 1}}\left( {2/\sqrt 3 } \right)$
  3. ${\tan ^{ - 1}}\left( {\sqrt 3/2 } \right)$
  4. ${\tan ^{ - 1}}\left( 2 \right)$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In the train frame, pseudo force ma acts down the plane. Resolving forces perpendicular and parallel to the ceiling gives the effective angle of the string with the normal to the ceiling. With acceleration a = g/2 up an incline of 30 degrees, the angle evaluates correctly to tan^(-1)(2 / sqrt(3)).

Multiple choice physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

A man of mass 'm' stands on a weighing machine in a lift

List - I  List-II
(a) Lift moves up with uniform acceleration a  (d) mg
(b) Lift moves down with uniform acceleration a (e) m(g$+$a)
(c) Lift moves down with uniform velocity (f) m(g-a)
  1. $a\rightarrow e,b\rightarrow f,c\rightarrow d,$
  2. $a\rightarrow d,b\rightarrow f,c\rightarrow e,$
  3. $a\rightarrow d,b\rightarrow e,c\rightarrow f,$
  4. $a\rightarrow f,b\rightarrow d,c\rightarrow e,$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When the lift moves $UP$ with uniform acceleration $a$ $Pseudo$ force on the man is $ma$ downward.

Net downward force is $mg+ma$. Hence, $e$

When the lift moves $down$ with uniform acceleration $a$ $Pseudo$ force on the man is $ma$ upward.
Net downward force is $mg+ma$. Hence, $f$


When the lift moves down with $uniform \ velocity$, only force acting is gravity.

Hence net force on man is $mg$. Hence, $d$

Multiple choice physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

A man drops an apple in the lift. He finds that the apple remains stationary and does not fall. The lift is:

  1. Going down with constant speed

  2. Going up with constant speed

  3. Going down with constant acceleration

  4. Going up with constant acceleration
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As the apple is dropped, it is under free-fall meaning that the force of gravity is acting on it. With respect to the person inside the lift, the apple seems not to be falling Hence, the man and the lift must also be falling with the action of acceleration due to gravity i.e, a constant acceleration.

option - C is correct.

Multiple choice physics newton's laws of motion weightlessness application of newton's law of motion escape velocity

When a lift is going up with uniform acceleration, the apparent weight of a person is $W _{1}$
When the lift is stationary, his apparent weight is $W _{2}$
When the lift falls freely his apparent weight is $W _{3}$
When the lift is going down with uniform acceleration which is less than the acceleration due to gravity, his apparent weight is $W _{4}$
The increasing order of these four weights is

  1. $W _{1},W _{3},W _{2},W _{4}$
  2. $W _{3},W _{4},W _{2},W _{1}$
  3. $W _{3},W _{2},W _{4},W _{1}$
  4. $W _{2},W _{3},W _{4},W _{1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

When lift accelerates up, pseudo force acts downwards, hence it increases apparent weight. $W _{1}>mg$
When lift is stationary, $W _{2}=mg$
When lift falls freely, it accelerates with g downwards, causing an upwards pseudo force in the frame of the lift equal to mg. Hence total force is 0. So weight is 0. $W _{3}=0$
When lift accelerates down, pseudo force acts upwards,  hence it decreases apparent weight $W _{4}<mg$, but also the acceleration is less than g, therefore $W _{4}=m(g-a)>0$

Hence, $W _{3}<W _{4}<W _{2}<W _{1}$

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

Weightlessness experienced while orbiting the earth in a spaceship is the result of

  1. Inertia

  2. Accelaration

  3. Zero gravity

  4. Centre of gravity
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Weightlessness means that there is no reaction on a body from the floor. Since both the artificial satellite & the astronaut have same centripetal acceleration (as in a lift; which is falling freely, we does not feel any weight, because both lift & we fall with same acceleration). so the astronaut does not feel any weight inside the space craft

Multiple choice physics gravitation: planets and satellites weightlessness application of newton's law of motion escape velocity

Weightlessness experienced in a spaceship is due to

  1. absence of of inertia.

  2. absence of gravity.

  3. absence of accelerating force.

  4. free fall of the spaceship.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

It is a misconception that there is no gravity in space.
An astronaut experiences weightlessness due the fact that as the spacecraft revolves around the Earth, the astronaut is continuously falling towards the Earth. This is similar to what a person standing in an elevator, that is falling freely, would experience. The person would be weightless as the elevator falls.

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

The negative of the work done  by the conservative internal forces on a system equals to the change in 

  1. total energy

  2. Kinetic energy

  3. Potential energy

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

The negative of the work done  by the conservative internal forces on a system equals to the change in potential energy


Hence, correct answer is option $C$

Multiple choice physics the essence of change forms of energy and energy conservation energy for everything forms of energy

Which of the following may no be conserved for an isolated system 

  1. Energy

  2. Potential energy

  3. Mechanical energy

  4. Kinetic energy
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Explanation

In an isolated system only $T.E$ is conserved $M.E$ can not be conserved in case of inelastic collision$.$ Some energy is converted into heat$.$ and sum of $P.E,K.E$ and lost energy remains const$.$

Hence,
option $b,c,d$ is correct answer.