## Motion in One Dimension | Chapter 2 | ICSE

**Q. When is a body said to be at rest?**

Ans: A body is referred to be in a state of rest or stationary when there is no change in the position of the body with respect to its immediate surroundings.

**Q. When is a body said to be in motion?**

Ans: A body is referred to be in a state of motion when there are changes in the position of the body with respect to its immediate surroundings.

**Q. Define displacement.**

Ans: Displacement is the shortest distance from the initial to the final position of the body.

S.I unit of displacement is the meter (m).

**Q. Define velocity.**

Ans: Velocity is defined as the distance covered per unit time by a body in a particular direction.

S.I. unit of velocity is m/s

**Q. Define speed.**

Speed is defined as the rate of change of distance with respect to time.

S.I. unit of speed is m/s

**Q. Define acceleration.**

Ans: Acceleration is defined as the rate of change of velocity with time.

S.I unit of acceleration is m/s^{2}

**Q. What is retardation?**

Ans: Negative of acceleration is called retardation.

Its SI unit is m/s^{2}

**Q. If a particle is moving in a circle, after one revolution, the distance will be the perimeter of the circle. What would be the displacement of the particle?**

Ans: zero.

**Q. What is Average Velocity?**

Ans: Average velocity is defined as the change in position or displacement divided by the time intervals in which the displacement occurs.

**Q. How can average velocity be zero?**

Ans: If a trip starts and ends at the same point, the total displacement is zero, so the average velocity is zero.

**Q. Can average velocity be zero?**

Ans: The average velocity can be positive or negative depending upon the sign of the displacement.

**Q. Is Average velocity a vector or a scalar?**

Ans: Average velocity is a vector quantity.

**Q. How can average velocity be identified?**

Ans: To calculate the average velocity, we need to divide the total displacement by the total time elapsed.

**Q. Define one-dimensional motion.**

Ans: The motion of a body is a one-dimensional motion if it moves along a straight line.

**Q. Can the speed of the body change if its velocity is constant?**

Ans: If the velocity of a body is constant, it means the magnitude and direction of the velocity do not change. Since the magnitude of the velocity is speed, the speed of the body cannot change.

**Q. When velocity is constant, does the average velocity over any interval of time differ from the instantaneous velocity?**

Ans: No, average velocity over an interval of time is equal to the instantaneous velocity, provided the velocity of a body is uniform or constant.

**Q. What are physical quantities? Give example.**

Ans: A physical quantity is a type of quantity that can be measured.

Eg: length, mass, time, pressure, temperature, current, resistance etc

**Q. What are scalar quantities?**

Ans: The physical quantities which have only magnitude are known as scalar quantities.

Eg: distance, speed, mass etc

**Q. What are vector quantities? Give example.**

Ans: The physical quantities for which both magnitude and direction are defined distinctly are known as vector quantities.

Eg: weight, velocity, displacement etc

**Q. What are uniform and non uniform speed?**

Ans: An object is said to be travelling with uniform speed if it covers equal distances in equal interval of time.

An object is said to be travelling with non uniform speed if it covers unequal distances in equal interval of time.

**Q. What is instantaneous speed?**

Ans: When the speed of an object is constantly changing, the instantaneous speed is the speed of an object at a particular moment in time.

**Q. What is uniform velocity?**

Ans: If a body covers equal distances in equal intervals of time in a given direction, then it is said to be uniform velocity.

**Q. What is instantaneous velocity?**

Ans: Instantaneous velocity is defined as the rate of change of position for a time interval which is very small or almost zero.

**Q. What is uniform acceleration?**

Ans: When an object is traveling in a straight line with an increase in velocity at equal intervals of time, then the object is said to be in uniform acceleration.

Free falling of an object is an example of uniform acceleration

**Q. Write the differences between scalar and vector quantities.**

Ans:

Scalar Quantity | Vector Quantity |

It has only the magnitude | It has direction and magnitude |

Only one dimensional | It is multidimensional |

This quantity changes with the change in magnitude | This changes with magnitude and direction |

Normal rules of algebra are applicable here | There is a different set of rules known as vector algebra |

One scalar quantity can divide another scalar | One vector cannot divide another vector |

**Q. Can displacement be zero even if the distance is not zero? Give one example to explain your answer.**

Ans: Yes, displacement can be zero even when distance is not zero

Example:- when a body travels in a circular path, after covering a circle the distance cannot be zero, but its displacement is zero.

**Q. When is the magnitude of the displacement equal to the distance?**

Ans: The magnitude of displacement is equal to the distance when the motion is in one direction.

**Q. Write the difference between acceleration and retardation.**

Ans:

Acceleration | Retardation |

Acceleration is known as the increment in velocity of a body per unit of time | Retardation is the reverse of acceleration. |

Acceleration can be positive or zero | Negative acceleration is known as deceleration or retardation. |

**Q. Define the term acceleration due to gravity. State its average value.**

Ans: It can be defined as the acceleration produced by a body when it is falling freely under gravity. The acceleration is produced as a result of earth’s gravitational attraction.

The average value of ′g′ is 9.8 ms^{−2 }

**Q. When does instantaneous speed equal average speed?**

Ans: At any point of time, instantaneous speed will be equal to the average speed only if the body moves with a uniform speed throughout.

**Q. Distinguish between uniform velocity and variable velocity.**

**Ans: **

UNIFORM VELOCITY | VARIABLE VELOCITY |

If the displacements covered by a body in equal intervals of time are the same then its velocity is said to be a uniform velocity | If the displacements covered by a body in equal intervals of time are not equal, then its velocity is said to be variable velocity. |

The velocity of a body remains uniform if there is no change in magnitude or direction. | The velocity of a body is variable due to the change in its magnitude or direction or both. |

If a body moves with uniform velocity its acceleration is zero. | If the body moves with variable velocity It has some acceleration |

**Q. State the difference between uniform motion and non-uniform motion.Answer:**

Non-uniform motion | Uniform motion |

(i) If the speed of an object moving along a straight line keeps changing, then this type of motion is called non-uniform motion. | (i) If the speed of an object moving along a straight line remains constant, then this type of motion is said to be uniform motion. |

(ii) In this case, average speed is generally different from the actual speed. | (ii) In this case, the average speed is same as the actual speed. |

(iii) The distance-time graph for non-uniform motion is a curved line. | (iii) The distance-time graph for uniform motion is a straight line. |

**Q. For the motion with uniform velocity, how is the distance travelled related to the time?**

Ans: For the motion with uniform velocity, distance is directly proportional to time

**Q. What information about the motion of a body are obtained from the displacement-times graph?**

Ans: The displacement-time graph gives us an idea about the motion of an object/body. With the help of a displacement-time graph, a slope can be obtained, through which we can fetch the value of the velocity of the body at any point of time that can also be used the velocity-time graph.

**Q. What can you say about the nature of motion of a body if its displacement-time graph is a straight line inclined to the time axis with an obtuse angle?**

Ans: it conveys that the motion is towards the reference or starting point, with a uniform velocity.

**Q. What can you say about the nature of motion of a body if its displacement-time graph is a straight line inclined to the time’s axis at an acute angle?**

Ans: it means its slope is fixed and positive. Hence the velocity is fixed and positive so it is a uniform motion in a straight line.

**Q. What can you say about the nature of motion of a body if its displacement-time graph is a non-linear curve.**

Ans: If the displacement-time graph is a curve, that means the velocity of the body is not uniform then the body is either accelerating or decelerating.

**Q. What can you say about the nature of motion of a body if its displacement-time graph is a straight line parallel to time axis ?**

Ans: If displacement-time graph is parallel to time axis, it means there is no change in displacement with time. Therefore, body is not in motion.

**Q. What does the slope of velocity-time graph represent?**

Ans: The slope of velocity-time graph gives acceleration.

Q. How is the distance related with time for the motion under uniform acceleration such as the motion of a freely falling body starting from rest?

Ans: S∝t^{2}