Motion MCQ Quiz - Objective Question with Answer for Motion - Download Free PDF

The correct answer is Instantaneous velocity.

Key Points

• Instantaneous velocity:
  • It is defined as the velocity of an object under motion at any given instant of time. So, option 1 is correct.
  • The SI unit of instantaneous velocity is m/s.
• The average velocity of an object is defined as its total displacement divided by the total time taken.
• Variable velocity is defined as the change of velocity with time.
• Uniform velocity: A body is said to have uniform velocity if it covers equal distance in equal intervals of time in a particular direction.

The distance traveled by an electromagnetic wave in one second is called wave speed or wave velocity.

 Additional Information

Wavelength(λ):

• The wavelength of a wave is the distance between successive crests of a continuous wave. The SI unit for wavelength is meters (m).

Frequency(f):

• The frequency of a wave is the measure of how many cycles of the wave completes every second. The SI unit of frequency is hertz (Hz).

Wave Speed Equation:

• The equation that calculates the speed, of a wave given its wavelength and frequency is:

Speed(v) = Wavelength(λ) x Frequency(f)

Period(T):

• The time taken by the wave to complete one oscillation. SI Unit of time period is seconds.

Amplitude:

• The maximum displacement of the wave from its mean or equilibrium position is called the amplitude of the wave.

• Running on a circular track have a maximum accelerated motion.
• Acceleration motion is the rate of change of velocity with time.
• The athlete moves with a constant speed, he is changing his direction with every single moment and the distance covered by a body in a unit time in a particular direction is called velocity.
• Therefore, it is an accelerated motion.

The correct answer is conservation of linear momentum.

Key Points

• The Jet engine works on the phenomenon of Conservation of Linear Momentum.
  • It produces a large volume of gases through the combustion of fuel, which is allowed to escape in a backward direction through a jet.
  • The backward rushing gas gains large momentum because of high velocity.
  • It thus imparts an equal and opposite momentum to the jet engine.
  • The jet engine, thus, moves forward at high speed.

Additional Information

• Momentum: Momentum is the product of the mass and the velocity of an object or particle. It is a vector quantity.
  • The standard unit of momentum magnitude is the kilogram-meter per second (kg·m/s).
    • P = m v
    • Where P = momentum, m = mass of the body, and v = velocity of the body.
• Conservation of Linear Momentum: Conservation of Linear Momentum states that a body in motion retains its total momentum (product of mass and vector velocity) unless an external force is applied to it.

CONCEPT:

• Momentum (p): The product of mass and velocity is called momentum. It is a vector quantity.
  • The SI unit of momentum is kg m/s.

Momentum (p) = Mass (m') × Velocity (v')

EXPLANATION:

Given that:

The mass of an object (m') is ½ m

The velocity (v') of an object  is 2v

We know that momentum (p) = mass × velocity = ((m/2) × 2 v) = m v​

• The momentum of the object is mv kg m/s. Hence option 4 is correct.

The correct answer is Newton's first law.

Key Points

• Newton's laws of motion-
  • ​Newton’s first law states that, if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by force.
    • This postulate is known as the law of inertia. The law of inertia was first formulated by Galileo Galilei for horizontal motion on Earth and was later generalized by René Descartes.
    • Before Galileo, it had been thought that all horizontal motion required a direct cause. Still, Galileo deduced from his experiments that a body in motion would remain in motion unless a force (such as friction) caused it to come to rest.
  • Newton’s second law is a quantitative description of the changes that a force can produce in a body's motion.
    • It states that the time rate of change of a body's momentum is equal in both magnitude and direction to the force imposed on it.
    • The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction.
    • A force applied to a body can change the magnitude of the momentum, direction, or both.
    • For a body whose mass m is constant, it can be written in F = ma, where F (force) and an (acceleration) are vector quantities.
    • If a body has a net force acting on it, it is accelerated by the equation. Conversely, if a body is not accelerated, there is no net force acting on it.
  • Newton’s third law states that when two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction.
  • The third law is also known as the law of action and reaction. This law is important in analyzing static equilibrium problems, where all forces are balanced, but it also applies to bodies in uniform or accelerated motion.
  • The forces it describes are real ones, not mere bookkeeping devices. For example, a book resting on a table applies a downward force equal to its weight on the table.
  • According to the third law, the table applies an equal and opposite force to the book. This force occurs because the book's weight causes the table to deform slightly so that it pushes back on the book like a coiled spring.

The correct answer is 342 m.

CONCEPT:

• Echo: If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
  • Echoes are heard due to the phenomenon of Reflection of sound waves.
  • To hear the echo clearly, the reflecting object must be more than 17.2 m from the sound source for the echo to be heard by a person standing at the source.

CALCULATION:

Speed of sound = 342 m/s.

The time is taken for hearing an echo = 2s.​

• The speed of sound is

\(⇒ Speed (v)= \frac{distance (d)}{time (t)}\)

Distance travelled = 2d = v × t

⇒ 2 × d = 342 × 2

⇒ d = (342 × 2)/2

The correct answer is To increase friction.

CONCEPT:

• Friction: Friction is a contact force when two surfaces interact. 
• Friction, a force that resists the sliding or rolling of one solid object over another.

EXPLANATION:

• Insoles of the shoes, they are treated to make their surface rough so that the frictional force is increased when they are used.
• The tyres of the vehicle are also treaded to increase friction and prevent slipping.
• For example, tires are treaded to reduce the risk of slipping and increase friction during the rainy or wet road, the same case is true for treaded shoes.

Important Points

• Friction finds application during matchsticks are ignited.
• The motion of pistons in a cylinder is an application of friction.
• It is possible to write on books and board because there is friction between the pen and the board.

The correct answer is Speed is constant.

Key Points

• Circular motion is a movement of an object along the circumference of a circle or rotation along a circular path.
• The distance and displacement are different at every instance at any particular point of time.

Confusion Points

• While the speed is a scalar quantity, in uniform motion, it remains constant.
• As, Velocity is a vector quantity, and the direction of movement changes continuously, velocity changes continuously.
• Due to this, the object is in accelerated motion.

Important Points

About the Circular Motion:

• As the direction of the velocity changes at every instant, it is an accelerated motion.
• During the motion, the particle repeats it's paths along the same trajectory.
• Thus the motion is periodic.

Uniform Circular Motion:

• During circular motion, if the speed of the period remains constant, it is a Uniform Circular Motion. Hence option 4 is correct.

CONCEPT:

• Work-energy theorem: It states that the sum of work done by all the forces acting on a body is equal to the change in the kinetic energy of the body i.e.,

Work done by all the forces = Kf - Ki

\(W = \frac{1}{2}m{v^2} - \frac{1}{2}m{u^2} = {\bf{Δ }}K \)

Where v = final velocity, u = initial velocity and m = mass of the body

CALCULATION:

It is given that,
Mass (m) = 4.0 kg

Final Velocity (v) = 5 m/s and initial velocity (u) = 0 m/s
According to the work-energy theorem,

⇒  Work done = Change in K.E
⇒  W = Δ K.E

Since initial speed is zero so the initial KE will also be zero.

⇒  Work done (W) = Final K.E = 1/2 mv²
⇒  W = 1/2 × 4 × 5²
⇒  W = 2 × 25
⇒  W = 50 J

The Correct Answer is 125 m.

Concept:

• The average acceleration for a given interval is defined as the velocity change for that particular interval of time.
• Unlike acceleration, for a given interval the average acceleration is determined.

\(a=\frac{\Delta v}{\Delta t}\)

Δv = Change in velocity

Δt = The duration of the period

Calculations:

Given that,

The initial velocity u = 18 km/h = 5 m/s

The final velocity v = 72 km/h = 20 m/s

Since the answer must be in m so, we need to convert

• Conversion of km/hr to m/s and vice versa-

18 km/hr converted to 18 × (5/18) = 5m/s

72 km/hr converted to 72 × (5/18) = 20 m/s

Time  = 10 sec

To find the distance travelled by car, we need to find acceleration,

\(a=\frac{\Delta v}{\Delta t}=\frac{change\; in\; velocity}{time}=\frac{20-5}{10}=1.5\;ms^{-2}\)

a = 1.5 m/s²

The distance travelled by car, we use the 2^nd equation of motion,

\(s=ut+\frac{1}{2}at^{2}\)

\(s=(5\times 10)+\frac{1}{2}(1.5)\times 10^{2}\)

s = (50 + 75) m

s = 125 m

The distance travelled by car is 125 m.

• The first equation of motion gives the relation between "velocity and time".
• The first equation of motion is v = u +at.
• Here, v is the final velocity, u is the initial velocity, a is the acceleration and t is the time.
• The velocity-time relation gives the first equation of motion and can be used to find acceleration.
• The position-time relation gives the second equation of motion, i.e. s = ut + (1/2) at²
• The position-velocity relation gives the third equation of motion, i.e. v² = u² +2as

Mass of body (m) = 50 kg

Acceleration (a) = 8 m/sec²

Time (t) = 15 seconds

According to kinematics equation, assuming acceleration is constant,

S = u t + 1/2 a t2 

Where

S = Distance travelled by the body (m)

u = Initial velocity (m/s)

a = Acceleration (m/s²)

t = Time taken

As body starts from rest u = 0 i.e. Initial velocity.

S = 0 + (1/2) × 8 × 15²  = 900m

S = 900 metres

The correct answer is Newton's first law.

CONCEPT:

• Newton’s first law of motion: It is also called the law of inertia. Inertia is the ability of a body by virtue of which it opposes a change.
• According to Newton’s first law of motion, an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.
• The inertia of rest: When a body is in rest, it will remain at rest until we apply an external force to move it. This property is called inertia of rest.
• The inertia of motion: When a body is in a uniform motion, it will remain in motion until we apply an external force to stop it. This property is called inertia of motion.

EXPLANATION:

• When a bus suddenly starts moving, the passengers fall backward due to the law of inertia of rest or 1st law of Newton.
• Because the body was in the state of rest and when the bus suddenly starts moving the lower body tends to be in motion, but the upper body still remains in a state of rest due to which it feels a jerk and falls backward. Hence option 1 is correct.

Additional Information

Laws of Motion given by Newton are as follows:

The correct answer is Velocity, time, and acceleration.

The first equation of motion gives the relation between initial velocity, final velocity, acceleration, and time.

• First equation of motion is given as v = u + at
  • Where, v = final velocity
  • u = initial velocity
  • a = acceleration
  • t = time taken

• The first equation of motion gives the value of velocity acquired by the body at any particular point of time t.
• The second equation of motion is given as s = ut + ½at²
• It gives the value of distance (s) traveled by a body at a given time t.
• Third equation of motion is given as v² = u² + 2as
• This equation gives the velocity of the body in traveling the distance s.