Conceptual Questions Based on Class 11 Physics Motion in A Straight Line

Here we are providing conceptual questions for Class 11 Physics Motion in A Straight Line. Answers are also provided along with questions. So that students can read and understand the question. These questions are prepared by the subject experts. Students can read these conceptual questions based on Motion in A Straight Line for better topic clarity and therefore will be able to score better marks in their exam.

Conceptual Questions Based on Class 11 Physics Motion in A Straight Line

Conceptual questions based on class Motion in A Straight Line is given below. Go through each and every question to understand the topic clearly.

Q.1. Can a particle in one-dimensional motion have zero speed and a non-zero velocity?

Solution. No, it the speed is zero, the velocity will be necessarily zero.

Q.2. Can a body exist in a state of absolute rest or of absolute motion? Explain.

Solution: Absolute rest and motion are unknown. In order to know whether the position of an object changes with time or not, a point absolutely fixed in space has to be chosen as reference point. But no such point is known in the universe. The earth revolves around the sun, the entire solar system travels through our own galaxy, the Milkyway and clusters of galaxies move with respect to other clusters. So, no object in the universe is in a state of absolute rest.

As no object in the universe is at absolute rest, so the absolute motion cannot be realised. Only relative rest and relative motion can be realised.

Q.3. What do you mean by motion in one, two and three dimensions? Give examples of each type.

Solution: One dimensional motion. The motion of an object is said to be one dimensional if only one of the three coordinates specifying the position of the object changes with time. Here the object moves along a straight line. This motion is also called rectilinear or linear motion.

Examples of one dimensional motion:

(i) Motion of a train along a straight track.

(ii) Motion of a freely falling body.

Two dimensional motion. The motion of an object is said to be two dimensional if only two of the three coordinates specifying its position change with time.

Examples of two dimensional motion:

(i) Motion of planets around the sun.

(ii) A car moving along a zig-zag path on a level road. Three dimensional motion. The motion of an object is said to be three dimensional if all the three coordinates specifying its position change with time.

Q.4. Can the displacement be greater than the distance travelled by an object? Give reason.

Solution. No, the displacement of an object can be either equal to or less than the distance travelled by the object. This is because displacement is shortest distance between the initial and final positions of the object while distance travelled is the length of the actual path traversed by the object.

Q.5. Can a body have a constant velocity and still have a varying speed?

Solution. No, a body cannot have a constant velocity while having a Varying Speed. Whenever the speed changes, velocity’ also changes.

Q.6. What is meant by a point object? Give suitable examples.

Point object. If the position of an object changes by distances much greater than its own size in a reasonable duration of time, then the object may be regarded as a point object. When a point object moves, its rotational and vibrational motions may be ignored.

Examples:

(i) Earth can be regarded as a point object for studying its motion around the sun.

(ii) A train under a journey of several hundred kilometres can be regarded as a point object.

Q.7. When does a cyclist appear to be stationary with respect to another moving cyclist?

Solution. When both the cyclists are moving in the same direction with the same velocity parallel to each other.

Q.8. Can an object have an eastward velocity while experiencing a westward acceleration?

Solution. Yes. A pendulum oscillating in east-west direction will have eastward velocity and westward acceleration in half cycle of its oscillation.

Q.9. Can the earth be regarded as point object when it is describing its yearly journey around the sun?

Solution. Yes, because size of the earth is much smaller than the distance from the sun.

Q.10. Can the direction of velocity of an object change, when acceleration is constant?

Solution. Yes. for an object thrown vertically upwards, the direction of velocity changes during its rise and fall. But acceleration acts always downwards and remains constant.

Q.11. When an observer is standing on earth, the trees and houses appear stationary to him. However, when he is sitting in a moving train, all these objects appear to move in backward direction. Why?

Solution. For the stationary observer, the relative velocity of trees and houses is zero. For the observer sitting in the moving train, the relative velocity of houses and trees is negative. So, these objects appear to move in backward direction.

Q.12. Is it possible for a body to be accelerated without speeding up or slowing down? If so, give an example.          

Solution. Yes. An object in uniform circular motion is accelerating but its speed neither decreases nor increases.

Q.13. Can a body have zero velocity and still be accelerating?  

Solution, yes. A body thrown vertically upwards has zero velocity at its highest point but has acceleration equal to the acceleration due to gravity.

Q.14. Two balls of different masses (one lighter and other heavier) are thrown vertically upward with same initial speed. Which one will rise to the greater height?                               

Solution. Both the balls will rise to the same heights. It is because, for a body moving with given initial velocity and acceleration, the distance covered by the body does not depend on the mass of the body.

Q.15. Can a body have a constant speed and still have a varying velocity?

Solution. Yes, a particle m uniform circular motion has a constant speed but varying velocity because of the change in its direction or motion at every’ point.

Q.16. Two balls of different masses (one lighter and other heavier) are thrown vertically upwards with the same speed. Which one will pass through the point of projection in their downward direction with the greater speed?  

Solution. In case of motion under gravity, the speed with which a body returns back is always equal to the speed with which it is thrown up. Since expression for final speed does not involve mass, Both the balls will acquire the same speed.

Q.17. Even when rain is falling vertically downwards, the front screen of a moving car gets wet while the back screen remains dry. Why?

Solution. This is because the rain strikes the car in the direction of relative velocity of rain with respect to car.

Q.18. Can the speed of a body be negative?

Solution. No, because the speed of an object is the distance travelled per unit rune and distance travelled is never negative.

Q.19. Can the relative velocity of two bodies be greater than the absolute velocity of either body?

Solution. Yes. When two bodies move in opposite directions, the relative velocity of each is greater than the individual velocity of either body.

Q.20. Is the direction of acceleration same as the direction of velocity?

Solution. Not necessarily. If velocity increases, acceleration acts in the direction of velocity and if velocity decreases, then acceleration acts in the opposite direction of velocity.

Q.21. A car travelling with a velocity of 50 km/hr on a straight road is ahead of a motor-cycle travelling with a speed of 75 km/hr. How would the relative velocity be altered if motor cycle is ahead of car?

Solution. The relative velocity will remain same as it does not depend on the position of the two bodies.

Q.22. Is it possible that the brakes of a car are so perfect that the car stops instantaneously. If not, why?

Solution. No, it is not possible. In order to make velocity zero in an infinitesimally small interval of time, the car needs an infinite declaration which is not possible.

Q.23. Is it possible to have a constant rate of change of velocity when velocity changes Both in magnitude and direction? If yes, give one example.

Solution. Yes, in projectile motion, a body has uniform acceleration in the downward direction while its velocity changes Both in magnitude and direction at every point of its trajectory

Q.24. Under what condition is the average velocity equal to the instantaneous velocity?

Solution. When a body moves with a constant velocity, its average velocity over any time interval is same as is instantaneous velocity.

Q.25. Can we use the equations of kinematics to find the height attained by a body projected upwards with any velocity?

Solution. No. The equations of kinematics are applicable only so long as the acceleration is uniform. The acceleration due to gravity is uniform only near the surface of the earth.

Q.26. If the displacement of a body is zero, is the distance covered by it necessarily zero? Comment with suitable illustration.

Solution. No, it is not necessary that the distance covered by a body is zero when its displacement is zero. Consider a particle moving along a circular track of radius r. After the particle completes one revolution, its displacement is zero while the distance covered is 2πr.

Q.27. State in the following cases, whether the motion is one, two or three dimensional:

(i) a kite flying on a windy day,

(ii) a speeding car on a long straight high way,

(iii) a carrom coin rebounding from the side of the board,

(iv) an insect crawling on a globe, and

(v)  a planet revolving around its star?

Solution.

(i) three-dimensional, (ii) one-dimensional,

(iii) two-dimensional, (iv) two-dimensional,

(v) two-dimensional.

Q.28. Why is the speed, in general, greater than the magnitude of the velocity?

Solution. Because of the change in the direction of motion, the length of the path traversed by a body is generally greater than the magnitude of its displacement. So, speed is generally greater than the magnitude of velocity.

Q.29. Distinguish between distance and displacement.         

Solution.

	Distance	Displacement
1.	Distance is the length of the actual path traversed by a body, irrespective of its motion.	Displacement is the shortest distance between the initial and final positions of body in a given direction.
2.	Distance between two points may be same or different for different paths chosen.	Displacement between two given points is always same.
3.	It is a scalar quantity.	It is a vector quantity.
4.	Distance covered may be positive or zero.	Displacement covered may be positive, negative or zero.

Q.30. Distinguish between speed and velocity.

Solution.

	Speed	Velocity
1.	It is the distance travelled by a body per unit time in any direction.	It is the distance travelled by a body per unit time in a fixed direction
2.	It is a scalar quantity.	It is a vector quantity.
3.	Speed may be positive or zero but never negative.	Velocity may be positive, negative or zero.

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Conceptual Questions Based on Class 11 Physics

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