Motion in a Straight Line: Important Concepts & MCQs

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Motion is a constant force in the universe. When there is a displacement in an object from its original position the motion is said to be done. Motion in a straight line refers to displacement of the object in a straight line. For example, motion of a lift is linear motion. It only moves up and down. Also, there are 2 types of linear motion; uniform linear motion and non-uniform linear motion. In a uniform motion the object moves with zero acceleration and constant velocity whereas in non-uniform motion the velocity varies and acceleration non-zero.

Ques 1. Which of the following are obtained by dividing total displacement by total time taken?

Average velocity
Instantaneous velocity
Uniform velocity
Speed

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Ans. (a) Average velocity

Explanation: The average velocity is obtained by dividing total displacement by total time taken. Instantaneous velocity is calculated at an instant and not over a period of time. Speed is distance divided by time. Velocity is said to be uniform when velocity at every instant is equal to the average velocity.

Ques 2. When a body is in the state of complete rest, what kind of energy does it possess?

Potential energy
Kinetic energy
Total energy
Heat energy

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Ans. (a) Potential energy

Explanation: When the body is in the state of rest, there is no motion. Hence there is no kinetic energy, hence the total energy of the body is stored as its potential energy. The total energy is the sum of kinetic and potential energies.

Ques 3. A car, initially at rest, travels 20 m in 4 sec along a straight line with constant acceleration. Find the acceleration of the car.

4.9 m/s²
2.5 m/s²
0.4 m/s²
1.6 m/s²

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Ans. (b) 2.5 m/s²

Explanation: Given: Initial velocity (u) = 0

Distance (s) = 20m

Time (t) = 4 sec

Now, S = ut + ½ at²

\ 20 = (0 x 20) + ½ x a x 4²

20 = 0 + ½ x a x 4²

Therefore, Acceleration (a) = 20/8 = 2.5 m/s2

Ques 4. A ball is dropped from a height of 80m. The distance travelled by it in the fourth second will be ___.

(g = 10 m/s²)

50 m
15 m
80 m
35 m

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Ans. (d) 35 m

Explanation: Distance travelled by a body in nth second is;

Sn = u + a/2 (2n – 1)

Given: The ball is dropped from 80 m height, so initial velocity (u) = 0 m/s

Acceleration due to gravity (a) = 10 m/s²

n = 4

For nth second,

Sn = u + a/2 (2n – 1)

Therefore,

Distance travelled in 4th second (S4) = 0 + 10/2 (2 x 4 – 1)

= 35 m

Ques 5. The slope of the velocity – time graph for retarded motion is

Zero
Positive
Negative
Neutral

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Ans. (c) Negative

Explanation: The slope of any graph is the ratio of the vertical change between two points to the horizontal change between the same points.

In velocity-time graph the velocity (v) is on the vertical axis and time (t) on the horizontal axis.

Hence, the slope is given by Slope = Dv/Dt

The rate of change of velocity is called acceleration; the slope of a velocity-time graph gives the acceleration.

The slope of the velocity-time graph for retarded motion is negative.

Ques 6. A body starts from rest and travels with a uniform acceleration of 20 m/s2. Calculate the time taken by the body to cover the distance of 90 m.

6s
3s
13s
12s

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Ans. (b) 3 s

Explanation: Given: acceleration (a) = 20m/s²

Distance travelled (s) = 90 m

Initial velocity (u) = 0

Time taken to cover 90 m is t

Now, S = ut + ½ at²

90 = 0 x t + ½ x 20 x t²

t2 = 9

Time taken (t) is 3 sec.

Read more about: Uniform Acceleration

Ques 7. The trajectory of an object is defined as x = (t-4)², what is the velocity at t = 5?

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Ans. (a) 2

Explanation: The function for velocity can be derived by differentiating the equation with respect to t.

v = 2 (t - 4) is the required function.

When t = 5, v = 2 (5 - 4)

v = 2

Ques 8. A car is moving in a spiral starting from the origin with uniform angular velocity. What can be said about the instantaneous velocity?

It increases with time
It decreases with time
It remains constant
It does not depend on time

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Ans. (a) it increases with time

Explanation: This type of motion can be called circular motion with increasing radius. As the radius increases, the tangential velocity increases (v = rw). Now, as there is only one velocity present, the speed will be equal to the magnitude of the tangential velocity.

Read more: Angular Velocity

Ques 9. If two bodies are moving in opposite directions with non-zero velocities, which of the following statements is true?

Relative velocity > Absolute velocity
Relative velocity < Absolute velocity
Relative velocity = Absolute velocity
Relative velocity <= Absolute velocity

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Ans. (a) Relative velocity > Absolute velocity

Explanation: The formula for relative velocity is, Vector VR = Vector VA – Vector VB. When both the velocities are opposite in direction, the equation becomes VR = VA – (-VB). Hence the magnitudes add up making the relative velocity greater than the absolute velocity of any of the two bodies.

Ques 10. What does relative motion signify?

The motion of a body with respect to other body
Uniformly accelerated
Non-uniformly accelerated
Motion along a curve

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Ans. (b) Uniformly accelerated

Explanation: The three equations of motion are valid for uniformly accelerated motion. The equations do not work in situations where the acceleration is non-uniform. In that case it is better to work with the differential forms of velocity and acceleration.

Ques 11. What is the rate of change of rate of change of displacement of a body?

Velocity
Acceleration
Force
Jerk

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Ans. (b) Acceleration

Explanation: The rate of change of displacement of a body is velocity. The rate of change of rate of displacement of a body, or rate of change of velocity is acceleration.

Ques 12. Displacement between two points is ___

The shortest path
The longest path
Equal to distance
Greater than distance

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Ans. (a) the shortest path

Explanation: Displacement between two points is the shortest path between them. It is always less than or equal to the distance between them. Displacement can never be greater than distance.

Ques 13. What will the velocity v/s time graph of a ball falling from a height before hitting the ground look like?

A straight line with positive slope
A straight line with negative slope
A straight line with zero slope
A parabola

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Ans. (a) a straight line with positive slope

Explanation: As the ball falls down, its velocity increases. This is because of the acceleration due to gravity. Hence the graph looks like a straight line with positive slope. The first equation of motion verifies this.

Ques 14. In a uniformly accelerated motion, the speed varies from 0 to 20 m/s in 4 s. What is the average speed during the motion?

10 m/s
20 m/s
0 m/s
15 m/s

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Ans. (a) 10 m/s

Explanation: From first equation of motion,

v = u + at

Where, a = 5 m/s².

From second equation of motion we have s = ut + (1/2)at²,

Where, s = 40 m.

Average speed = s/t = 40/4 = 10 m/s

Also read:

Acceleration and velocity	Speed-time graph	Newton’s third law of motion
Class 12 Physics Notes	class 11 physics notes	Physics Constants
Relation Between articles (Physics)	SI Units in Physics	Derivations in Physics
Difference between in physics	Physics Study Material	Physics Formula

Motion in a Straight Line: Important Concepts & MCQs

CBSE CLASS XII Related Questions

1.
The electric field at a point in a region is given by \( \vec{E} = \alpha \frac{\hat{r}}{r^3} \), where \( \alpha \) is a constant and \( r \) is the distance of the point from the origin. The magnitude of potential of the point is:

2.
Two point charges \( q_1 = 16 \, \mu C \) and \( q_2 = 1 \, \mu C \) are placed at points \( \vec{r}_1 = (3 \, \text{m}) \hat{i}\) and \( \vec{r}_2 = (4 \, \text{m}) \hat{j} \). Find the net electric field \( \vec{E} \) at point \( \vec{r} = (3 \, \text{m}) \hat{i} + (4 \, \text{m}) \hat{j} \).

5.
A current carrying circular loop of area A produces a magnetic field \( B \) at its centre. Show that the magnetic moment of the loop is \( \frac{2BA}{\mu_0} \sqrt{\frac{A}{\pi}} \).

6.
A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases.

Similar Physics Concepts

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Motion in a Straight Line: Important Concepts & MCQs

CBSE CLASS XII Related Questions

1.The electric field at a point in a region is given by \( \vec{E} = \alpha \frac{\hat{r}}{r^3} \), where \( \alpha \) is a constant and \( r \) is the distance of the point from the origin. The magnitude of potential of the point is:

2.Two point charges \( q_1 = 16 \, \mu C \) and \( q_2 = 1 \, \mu C \) are placed at points \( \vec{r}_1 = (3 \, \text{m}) \hat{i}\) and \( \vec{r}_2 = (4 \, \text{m}) \hat{j} \). Find the net electric field \( \vec{E} \) at point \( \vec{r} = (3 \, \text{m}) \hat{i} + (4 \, \text{m}) \hat{j} \).

3.A rectangular glass slab ABCD (refractive index 1.5) is surrounded by a transparent liquid (refractive index 1.25) as shown in the figure. A ray of light is incident on face AB at an angle \(i\) such that it is refracted out grazing the face AD. Find the value of angle \(i\).

5.A current carrying circular loop of area A produces a magnetic field \( B \) at its centre. Show that the magnetic moment of the loop is \( \frac{2BA}{\mu_0} \sqrt{\frac{A}{\pi}} \).

6.A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases.

Similar Physics Concepts

Comments

SUBSCRIBE TO OUR NEWS LETTER

1.
The electric field at a point in a region is given by \( \vec{E} = \alpha \frac{\hat{r}}{r^3} \), where \( \alpha \) is a constant and \( r \) is the distance of the point from the origin. The magnitude of potential of the point is:

2.
Two point charges \( q_1 = 16 \, \mu C \) and \( q_2 = 1 \, \mu C \) are placed at points \( \vec{r}_1 = (3 \, \text{m}) \hat{i}\) and \( \vec{r}_2 = (4 \, \text{m}) \hat{j} \). Find the net electric field \( \vec{E} \) at point \( \vec{r} = (3 \, \text{m}) \hat{i} + (4 \, \text{m}) \hat{j} \).

5.
A current carrying circular loop of area A produces a magnetic field \( B \) at its centre. Show that the magnetic moment of the loop is \( \frac{2BA}{\mu_0} \sqrt{\frac{A}{\pi}} \).

6.
A parallel plate capacitor has plate area \( A \) and plate separation \( d \). Half of the space between the plates is filled with a material of dielectric constant \( K \) in two ways as shown in the figure. Find the values of the capacitance of the capacitors in the two cases.