Motion in a straight line Important questions of physics || Linear motion important question || Short Questions || PHYSICS || KINEMATICS 1 D ||

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Ques 1: What is meant by a point object in physics?

Ans: An object is said to be a point object if it is dimensionless [MⁿLⁿTⁿ , n= 0]. And the path in which it travels is much larger in compare to the mass of the object. 

Ques 2: Is it true that a body is always at rest in a frame which is fixed to the body itself?

Ans: Yes, because relative velocity with respect to frame of reference is zero.

Ques 3: Discuss if a body moving with uniform velocity is in equilibrium.

Ans:  Net force on the body is zero. Net acceleration of the body is zero and the force is product of mass and acceleration. Hence, the net force on the body is zero. 

Ques 4: What does the speedometer records−the average speed or the instantaneous speed? 

Ans: It records (or measures) the instantaneous speed(Speed at a particular interval of time) at an instant of time.  

Ques 5: Which motion is exactly represented by ∆𝒔 = 𝒖∆𝒕.

Ans: It represents the motion with uniform velocity.



Ques 6: In which frame of reference is the body always at rest?

Ans: The body is always at rest in the frame attached to it, i.e., inertial frame of reference.

Ques 7: Can you think of a situation where a body falling under the gravity has constant velocity? Give example. 

Ans:  Yes, terminal velocity of a body. In the lift when the lift is moving with the constant velocity. 

Ques 8: Give an example of a motion which even though is accelerated motion yet it is called uniform motion. 

Ans: Uniform circular motion, in this body move constant speed but continuous changing its direction. It is also known as centripetal acceleration. 

Ques 9: How many dimensions of motion does the following have?

(a)Train moving fast on it track.

(b) A lizard moving on a wall in a room.

(c) Kite flying in the sky.

(d) Bee flying in a closed room.

Ans: (a) One dimensional motion

(b) Two-dimensional motion

(c) Three-dimensional motion

(d) Three-dimensional motion.

Ques 10: Under what condition the magnitude of average velocity of a particle is equal to the average speed? 

Ans: The magnitude of the average velocity of a particle is equal to the average speed if the particle moves along a straight line(Or the body is having the linear motion) in a fixed direction.

Ques 11: When the train in which you are sitting starts moving by the side of another train without jerks, you find that the other train is moving but when you look at the  platform you find that your train is moving. Name the phenomenon responsible for such a motion. 

Ans: Relative velocity is the phenomenon responsible for such a motion. 

Ques 12:  Two particles A and B are moving along the same straight line with B moving ahead of A. velocities remaining unchanged, what would be the effect on the  magnitude of relative velocity if A is ahead of B? When both the bodies are moving in the same direction  they are feeling the they are not moving or moving with little speed. Two particles A and B are moving along the same straight line with B moving ahead of A. velocities remaining unchanged,what would be the effect on the magnitude of relative velocity if A is ahead of B?

Ans. The magnitude of the relative velocity will remain same, i.e., no effect on its magnitude.

Ques 13: Why speed of an object cannot be negative? 

Ans: Speed of an object cannot be negative because the distance can never be negative and speed is a scalar quantity which is having only magnitude. Hence, Speed can't be negative. 

Ques 14: Can earth be regarded as a point object if only orbital motion of earth around the sun is considered? Why? 

Ans: Yes. This is because the size of earth is very small as compared to the size of the orbit of the earth around the sun. 

Ques 15: One light and another heavy masses are thrown vertically upward with same initial speed. Which will attain higher height? 

Ans: The height attained is independent of the mass of body so with same initial speeds both will attain same height. 

Ques 16: Two balls of different masses are thrown vertically upward with same initial velocity. Maximum heights attained by them are 𝐡 𝟏 and 𝐡 𝟐 respectively. What is 𝐡 𝟏 / 𝐡 𝟐?

Ans: Height attained by both the balls will be same as height attained a independent of masses. Therefore, h1/h2 = 1. 

Ques 17: A car moving with velocity of 50 km/h on a straight road is ahead of jeep  moving with velocity 75 km/h. How would the relative velocity be altered if jeep is ahead of car? 

Ans: There is no change in relative velocity. Because, both the cars are  moving in the same direction. 

Ques 18: Will the displacement of a particle change on changing the position of origin of the coordinate system? 

Ans. No, it will not change. Because, the position is the length between two points respectively. 

Ques 19: If the instantaneous velocity of a particle is zero, will its instantaneous acceleration be necessarily zero? 

Ans: No, it will no be zero because at highest point of vertical is zero but its instantaneous acceleration is not zero. 

Ques 20: What is d e-acceleration or retardation?

Ans: Negative acceleration is called retardation or de acceleration, i.e., when velocity of an object is steadily decreasing with respect to time then the object is said to have retardation.

Ques 21: What is represented by the slope of v - t graph?

Ans: Slope of v - t graph represent acceleration.

Ques 22:  stone is thrown vertically upwards from the surface of earth. What is the direction of the velocity and acceleration of the stone (a) on its upward motion, (b) on its downward motion? 

Ans (a) Velocity is vertically upward and acceleration (gravitational acceleration(g)) is vertically downward. 

(b) Both velocity and acceleration (g) are vertically downward.

Ques 23: The motion of two persons is shown by two straight lines on a displacement - time graph(s - t graph) intersecting each other a certain point. What information do you get from  the point of intersection? 

Ans: This means that the two persons cross each other at a certain place at a given instant of time.

Ques 24: An object falling through a fluid is observed to have acceleration given a =  g − b v where, g = gravitational acceleration and b is constant. After a long time of  release, it is observed to fall with constant speed. What must be the value of  constant speed? 

Ans. When a = 0, velocity of the particle became constant i.e., v = constant = v c.

Then from given equation a = g − b v 

0 = g - b v 

v = g / b

Ques 25: Two balls have same size but one is dense. When released simultaneously from same height which ball will reach the ground first?

Ans: Retardation (a) of the denser ball due to air resistance is less so (g − a) is more for the denser ball. Thus, denser ball would reach ground first.

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