Class 9 Science

Motion

In Text Question Answer

Part 2

Question 8: During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is, 3 × 108 ms-1.

Answer: Here, we have, speed `=3xx10^8\ ms^(-1)`

Time = 5 minute

`=5xx60s=300` second

We know that, Distance = Speed x Time

⇒ Distance `=300xx3xx10^8\ ms^(-1)`

`= 900 xx 10^8\ m`

`=9xx10^10m`

Question 9: When will you say a body is in

(i) uniform acceleration?

Answer: When rate of change of motion is same in equal intervals of time.

(ii) non-uniform acceleration?

Answer: When rate of change of motion is not same in equal intervals of time.

Question 10: A bus decreases its speed from 80 km/h to 60 km/h in 5 s. Find the acceleration of the bus.

Answer: Here we have, u=80 km/h `=80xx5/(18)=(200)/9` m/s

v=60 km/h `=60xx5/(18)=(50)/3` m/s and `t=5s`

∴ Acceleration (a) =?

We know that `v=u+at`

Or, `a=(v-u)/t`

`=((50)/3-(200)/9)/5=-(50)/(9xx5)`

`=-(10)/9` m s-2

Question 11: A train starting from a railway station and moving with uniform acceleration attains a speed of 40 km/h in 10 minutes. Find its acceleration.

Answer: Here we have,
Initial velocity, u = 0,
Final velocity, v = 40km/h `=40xx5/(18)=(100)/9` m/s
Time (t) = 10 minute = 60 × 10 = 600s
Acceleration (a) =?

We know that `v=u+at`

Or, `a=(v-u)/t`

`=(100)/(9xx600)=1/(54)` m s-2

Question 12: What is the nature of the distance-time graphs for uniform and non-uniform motion of an object?

Answer:

(a) The slope of the distance-time graph for an object in uniform motion is straight line.

(b) The slope of the distance-time graph for an object in non-uniform motion is not a straight line.

Question 13: What can you say about the motion of an object whose distance-time graph is a straight line parallel to the time axis?

Answer: When the slope of distance-time graph is a straight line parallel to time axis, the object is moving with uniform motion.

Question 14: What can you say about the motion of an object if its speed-time graph is a straight line parallel to the time axis?

Answer: When the slope of a speed time graph is a straight line parallel to the time axis, the object is moving with uniform speed.


Matter in Our Surroundings

Anything that has both mass and volume is called matter. You can also say that anything which has mass and which occupies space is called matter.

Is Matter Around Us Pure?

Elements and compounds are pure substances. All other substances are mixtures which means they are not pure substances.

Atoms and Molecules

Read about law of conservation of mass, law of constant proportions and Dalton's atomic theory.

Structure of Atoms

Atom is made of three particles; electron, proton and neutron. These particles are called fundamental particles of an atom or sub atomic particles.

Cell: The Fundamental Unit of Life

A cell is capable of independent existence and can carry out all the functions which are necessary for a living being.

Tissue

A groups of cells which is meant for a specific task is called tissue. Tissues are the first step towards division of labour in complex organisms.

Diversity in Living Organisms

Without proper classification, it would be impossible to study millions of organisms which exist on this earth.

Motion

If an object changes its position with respect to a reference point with elapse of time, the object is said to be in motion.

Force & Laws of Motion

Force has numerous effects. Force can set a stationary body in motion. Force can stop a moving body.

Gravitation

Earth attracts everything towards it by an unseen force of attraction. This force of attraction is known as gravitation or gravitation pull.

Work & Energy

When force is exerted on an object and object is displaced, work is said to be done. It means work is the product of force and displacement.

Sound

Sound is a type of energy. Sound travels in the form of wave from one place to another.

Why Do We Fall Ill

Health is a state of physical, mental and social well being. A condition in which the affected person is unable to carry out normal activities is termed as disease.

Natural Resources

Resources which are obtained from nature are called natural resources. Examples: Air, water, soil, wood, etc.

Improvement in Food Production

Food security is said to exist when all people, at all times, have physical and economic access to sufficient, safe and nutritious food to meet their dietary needs and food preferences for an active and healthy life.