Students should practice questions given in Motion Chapter 8 Class 9 Science Worksheets. These worksheets for Class 9 Science have a good collection of important questions and answers which are expected to come in your class tests and examinations. You should learn these solved worksheet questions for Science Class 9 as it will help you to understand all topics and give you more marks.

**Class 9 Science Worksheets Chapter 8 Motion**

Please refer to below questions and answers for Motion Chapter 8 Class 9 Science Worksheets. Prepared by expert teachers for Standard 9 Science

**Question. Give two examples of a vector quantity?**

## Answer

Two examples of a vector quantity are displacement and velocity.

**Question. Define acceleration. Is it a scalar or a vector quantity?**

## Answer

In non-uniform motion, the velocity of a body changes with time. It has different velocities at different instants of time and at different points of its path. In such a situation, we define a physical quantity called acceleration which is a measure of the change in the velocity of a body per unit time. It is a vector quantity.

**Question. What is the Si unit of acceleration?**

## Answer

The SI unit of acceleration is m/s^{2}.

**Question. Give two examples of a scalar quantity.**

## Answer

Two examples of a scalar quantity are distance and speed.

**Question. Define vector quantity.**

## Answer

A physical quantity which has both magnitude and direction is called a vector quantity.

**Question. Differentiate acceleration from velocity.**

## Answer

Velocity is the change in position of a body per unit time in a given direction and acceleration is the change in velocity of a body per unit time.

**Question.“The direction in which an object moves is given by the direction of velocity of the object and not the direction of acceleration.” Give an example to justify this statement.**

## Answer

When an object is thrown upward, its velocity is directed upward while its acceleration is directed downwards. Thus, the velocity determines the direction of motion.

**Question.Give the simplest type of motion.**

## Answer

The simplest type of motion is the motion along a straight line.

**Question.Define non-uniform acceleration. Give one example.****Answer.** Non-uniform acceleration : An object has non-uniform acceleration if it travels in a straight line and its velocity increases or decreases by unequal amounts in equal intervals of time.

For example : The movement of a car on a busy road has non-uniform acceleration.

**Question.A satellite revolves round the Earth with uniform speed. Is this motion accelerated? If so, in which direction does the acceleration act?****Answer. **The velocity of the satellite revolving around the Earth changes due to change in its direction of motion. So, the motion of satellite is an accelerated

one. The acceleration is directed towards the centre of the Earth.

**Question.When is the acceleration of a body is negative?****Answer.**The acceleration of a body is taken to be negative when it is opposite to the direction of velocity.

**Question.Define the following :****(i) Translatory motion****(ii) Complex motion****Answer.**

(i) When a body moves along a straight line, its motion is called rectilinear or translatory motion.

For example : A car moving on a straight road.

(ii) When a body has two or more types of motion, it is said to possess complex motion. For example : A ball rolling down on inclined planes has both rectilinear as well as circular motion.

**Question.(i) Give some examples of erratic and uncontrolled motion.****(ii) Give an example of controlled motion which can be a service to human beings.****(iii) Is there a need to study about the erratic which of some objects and learn to control them?****Answer.**

(i) Flooded river, a hurricane, a tsunami, etc.

(ii) Controlled motion of a river in a dam is useful to generate hydroelectric power.

(iii) Yes, we should study about the erratic motion of some objects because it will help us in disaster management.

**Question.What is the meant by retardation? Give its S.I. unit.****or****Give an example of negative acceleration.****Answer.** **Retardation :** When the velocity of a body decreases with time, its final velocity is less than the initial velocity, i.e. its acceleration is negative. This negative acceleration is called retardation. The S.I. unit of retardation is ms^{ 2}.

Example : When brakes are applied to a moving car, its velocity gradually decreases. Under these conditions, the car is under retardation.

**Question.How does the velocity change with time in uniform rectilinear motion of an object?****Answer.** In uniform rectilinear motion of an object, the velocity is constant with time, i.e. change in velocity of the object during any time interval is zero.

**Question.****(i) Give an example of motion in human body which cannot be perceived directly.****(ii) Give an example of motion in nature which cannot be perceived directly.****(iii) Give an example of motion of the Earth which cannot be perceived directly.****Answer.**

(i) The motion of blood through veins and arteries in human body cannot be perceived directly.

(ii) The motion of air is not perceived directly. We perceive it by observing the movement of dust or leaves of trees, etc.

(iii) The phenomena of sunrise, sunset and change of seasons is due to rotation and revolution of the Earth which cannot be perceived directly.

**Question.How does the velocity change with time in nonuniform rectilinear motion of an object?****Answer.** The velocity has different values at different instant of time and at different points of its path, i.e. change in velocity of the object during any time interval is not zero.

**Question.How can we represent the change in the position of an object with time?****Answer.** The change in the position of an object with time can be represented on the distance-time graph by adopting a convenient scale of choice.

In this graph, time is taken along x-axis and distance is taken along y-axis.

**Question.A person moves along the boundary of a square field of side 10 m in 20 s. What will be the magnitude of displacement of that person at the end of 2 minutes 20 seconds?****Answer.**

Side of square field = 10 m

So, perimeter = 10 m × 4 = 40 m

Person moves along the boundary in 20 sec.

Displacement after 2 m 20 sec

= 2 × 60 s + 20 s = 140 s = ?

Since in 20 s person moves 40 m.

Therefore, in 1 sec distance covered 40/20 = 2 m

Therefore, in 140 sec distance covered

= 2 × 140 = 280 m

Now, number of rotation to cover 240 along the boundary

= Total distance/Perimeter

= 280m/40m = 7 rounds.

Hence, after 7 rounds the person will be at the starting point, so displacement will be zero.

**Question.Neha swims in a 90 m long pool. She covers 180 m in one minute by swimming from one end to the other and back along the same straight path. Find the average speed and average velocity of Neha.****Answer.**

Total distance = 180 m

Total displacement = 0

Time taken t = 1 min = 60 s

Average speed (Vav) = Total distance/Total time taken

=180m/60s = 3m/s

Average velocity (Vav) = Displacement/Total time taken

= 0/60 s = 0 m/s

**Question.A car decreases its speed from 80 km/h to 60 km/h is 5 seconds. Find the acceleration of the car.****Answer.**

u = 80 km/h = 80 × 5/18 = 22.22 m/s

v = 60 km/h = 60 × 5/18 = 16.67 m/s

Time (t) = 5 s

–1.11 m/s^{2}

**Question.A train starting from a railway station and moving with uniform acceleration, attains a speed 40 km/h in 10 minutes. Find its acceleration.****Answer.**

u = 0 (starting from rest)

v = 40 km/h= 11.11 m/s

Time t = 10 minutes = 600 s

**Question.The average speed of a bicycle, an athlete and car are 18 km/h, 7 m/s and 2 km/min respectively. Which of the three is the fastest and which is the slowest?****Answer.**

Thus, the average speeds of the bicycle, the athlete and the car are 5 m/s, 7 m/s and 33.3 m/s respectively.So, the car is the fastest and the bicycle is the slowest.

**Question.Figure shows distance-time graph of two objects A and B, which object is moving with greater speed when both are moving?****Answer.**

The line for object B makes a longer angle with the time-axis. Its slope is longer than the slope of the line for object A. Thus, the speed of B is greater than that of A.

**Question.Figure represents the speed time graph for a particle.****Find the distance covered by the particle between t = 10 min and t = 30 min.**

**Answer.**

We draw perpendicular lines from the 10-minute point and the 30-minute point to the time-axis (fig.). The distance covered is equal to the area of the rectangle ABCD, its value is

ABCD = (30 min – 10 min) x (10 km/h)

= 20 min × 10 km/h