9th Class (CBSE) Science: Motion

Question: Define  uniform motion.

Answer: When an object covers equal distances in equal intervals of time, it is said to be in uniform motion.

Question: Define speed.

Answer: It is defined as the distance traveled by an object in unit time. Its unit is m/s.

Question: Define velocity.

Answer: Velocity is the speed of an object moving in define direction.

Question: Define acceleration.

Answer: Change in the velocity of an object per unit time.

a = v – u/t, S.I. unite is m/s^-2.

Question: While plotting a distance-time graph, why do we plot time on X- axis.

Answer: While plotting a distance-time graph, we should plot time on X- axis as, all independent quantities are plotted on X-axis.

Question: What is odometer?

Answer: Odometer is a device fitted in the automobiles to show the distance traveled.

Question: What does the area under velocity-time graph represent?

Answer: The area under the velocity-time graph represents the displacement.

Question: A body travels a distance from A to B its physical quantity is measured ti be – 15 m/s. Is it speed or velocity? Give reason for the answer.

Answer: The physical quantity is – 15 m/s. It represents velocity because sign of speed cannot be a negative. Negative sign indicates the opposite direction.

Question: What type of velocity-time graph will you get for particle moving with a constant acceleration?

Answer: For a particle moving with a constant acceleration velocity-time graph will be a straight line inclined to x-axis.

Question: Define uniform circular motion.

Answer: When a body moves in a circular path with uniform speed, its motion is called uniform circular motion.

Question: What is deceleration?

Answer: When the speed of an object decreases, the object in said to be decelerating. In this case the direction of acceleration is opposite to the velocity of the object.

Question: Give the difference between distance and displacement.

Answer: Distance:

1. It is the total path covered by an object.
2. It does not need direction.
3. It cannot be ‘0’.

Displacement:

1. It is the displacement of the body per unit time.
2. It is a vector quantity, direction is required.
3. It can be ‘0’.

Question: Give the difference between speed and velocity.

Answer: Speed:

1. It is the distance traveled by an object per unit time.
2. It is scalar quantity, direction not required.
3. Its unit is m/s and is always positive.

Velocity:

1. It is the displacement of the body per unit time.
2. It is a vector quantity, direction is required.
3. Its unit is m/s and can be negative.

Question: Give the difference between acceleration and deceleration.

Answer: Acceleration:

1. It is change in velocity per unit time. It is always positive.
2. In this case, the velocity keeps increasing.
3. u < v, initial velocity is less than final velocity u = 0.

Deceleration:

1. It is change in velocity per unit time. It is always negative.
2. In this case the the increased velocity starts decreasing.
3. u < v, final velocity is less than initial velocity u = 0.

Question: Differentiate between velocity and acceleration.

Answer: Velocity:

1. The rate of change of position of a body is called velocity.
2. S.I. unit is m/s.

Acceleration:

1. It is the rate of change of velocity.
2. S.I. unit is m/s^-2.