Living Science Physics Class 7 ICSE Solutions Chapter 2 Motion

ICSE Living Science Physics for Class 7 Solutions Chapter 2 Motion

Think And Answer (Page 18)

Question 1.
There are two children riding a bicycle with the same speed on a straight road. Explain whether these children are at rest or in motion.
Answer:
The children are said to be at rest with respect to each other. However, they are said to be in motion with respect to the surroundings.

Check Your Progress (Page 22)

Write true or false. Correct the false statements.
Question 1.
Rest and motion are relative terms.
Answer:
True.

Question 2.
Rectilinear and curvilinear motions are two types of rotatory motion.
Answer:
False. Rectilinear and curvilinear motions are two types of translatory motion.

Question 3.
During rotatory motion, all parts of the moving object moves through the same distance in the same interval of time.
Answer:
True.

Question 4.
The motion of a cricket ball bowled by a spin bowler is an example of oscillatory motion.
Answer:
False. The motion of a cricket ball bowled by a spin bowler is an example of combination motion.

Question 5.
A motion that repeats itself at regular intervals of time is called non-periodic motion.
Answer:
False. A motion that repeats itself at regular intervals of time is called periodic motion.

B. Fill in the blanks.

1. ………… is the ratio of the total distance travelled to the total time taken.
Answer:
Speed is the ratio of the total distance travelled to the total time taken.

2. The distance travelled by a body is a …………. quantity whereas its displacement is a quantity.
Answer:
The distance travelled by a body is a scalar quantity whereas its displacement is a vector quantity.

3. If a person walks 10 m due south in 10 seconds, 10 m due east in the next 10 seconds and 10 m due north in the next 10 seconds, then he has ………….. velocity.
Answer:
If a person walks 10 m due south in 10 seconds, 10 m due east in the next 10 seconds and 10 m due north in the next 10 seconds, then he has non-uniform velocity.

4. If an object covers …………. distances in …………… intervals of time along a straight line, it is said to have a uniform motion.
Answer:
If an object covers equal distances in equal intervals of time along a straight line, it is said to have a uniform motion.

5. …………. of a body is the distance travelled by it per unit time whereas its …………… is the distance travelled by it per unit time in a given direction.
Answer:
Distance of a body is the distance travelled by it per unit time whereas its displacement is the distance travelled by it per unit time in a given direction.

A. Tick the most appropriate answer.

Question 1.
A car parked in a parking lot is said to be in/at
a. rest.
b. motion.
c. uniform speed.
d. uniform velocity.
Answer:
a. rest.

Question 2.
A bullet launched from a toy gun is an example of
a. rectilinear motion,
b. curvilinear motion.
c. circular motion.
d. oscillatory motion.
Answer:
b. curvilinear motion.

Question 3.
The motion of a spinning top is an example of
a. random motion
b. curvilinear motion.
c. rotatory motion.
d. oscillatory motion.
Answer:
c. rotatory motion.

Question 4.
The nature of the motion of the earth around its axis is
a. rectilinear
b. curvilinear.
c. rotatory
d. random.
Answer:
c. rotatory.

Question 5.
Which of the following is a vector quantity?
a. distance
b. density
c. speed
d. displacement
Answer:
d. displacement

Question 6.
A body moves 3 km due west and then 4 km due north. The displacement of the body is –
a. 5 km towards south.
b. 5 km towards south-west.
c. 5 km towards North.
d. 5 km towards North-west.
Answer:
d. 5 km towards North-west.

Question 7.
Which of the following relations is correct?

Answer:

Question 8.
n object moves for 50 seconds at a speed of 20 m/s. What is the distance travelled by the car ?
a. 100 m
b. 10,000 m
c. 1000 m
d. 1000 km
Answer:
c. 1000 m

Question 9.
The mass of a body
a. changes with place
b. changes with time
c. remains the same.
d. can be zero.
Answer:
c. remains the same.

Question 10.
Which of the following instruments is used to measure weight?
a. spring balance
b. beam balance
c. stopwatch
d. thermometer
Answer:
a. spring balance

B. Fill in the blanks.

Question 1.
A disc thrown by an athlete is an example of ………….. motion.
Answer:
A disc thrown by an athlete is an example of combination motion.

Question 2.
An object moving on a curved path is said to have …………..
Answer:
An object moving on a curved path is said to have curvilinear motion.

3. ………….. is the shortest distance between the initial and
final positions of a body.
Answer:
Displacement is the shortest distance between the initial and final positions of a body.

4. The SI unit of velocity is ………….
Answer:
The SI unit of velocity is ms^-1

Question 5.
The of a body is defined as the quantity of matter contained in it.
Answer:
The mass of a body is defined as the quantity of matter contained in it.

C. Match the columns.

1. Displacement	a. metre per second
2. Velocity	b. kilogram
3. Time	c. metre
4. Mass	d. newton
5. Weight	e. second

Answer:

1. Displacement	c. metre
2. Velocity	a. metre per second
3. Time	e. second
4. Mass	b. kilogram
5. Weight	d. newton

D. Answer the following in short.

Question 1.
Define translatory motion.
Answer:
If an object moves in a line in such a way that every part of the object moves through the same distance in the same time interval, then the object is said to be in translatory motion. It is of two types – rectilinear and curvilinear.
Examples : Apple falling from a tree, earth moving around the sun.

Question 2.
What do you understand by oscillatory motion ?
Answer:
When an object as a whole moves to and fro about its mean position, it is said to be in oscillatory motion.
Examples : a swing in motion, a moving pendulum, etc.

Question 3.
What do you understand by a vector quantity ?
Answer:
A physical quantity that needs both magnitude and direction to be described is called a vector quantity.
Examples : Displacement, velocity, acceleration, force and weight.

Question 4.
A child moves a toy car, takes it around and brings it back to the starting point. What is the displacement of the car?
Answer:
As the car is brought back to its starting point, the displacement is zero.

Question 5.
A car is moving at the rate of 40 km/h towards east. Which physical quantity is stated here, speed or velocity?
Answer:
Velocity, since it is mentioning the direction of motion along with its speed.

E. Answer the following in detail.

Question 1.
What do you understand by the term motion ?
Answer:
An object is said to be in motion if it changes its position with respect to a certain fixed reference point in its surroundings.

Question 2.
Speed and velocity have the same units yet they are different physical quantities. Why?
Answer:
Speed does not depend upon direction so it is a scalar quantity whereas velocity depends upon the direction of displacement so it is a vector quantity.

Question 3.
Explain why a car driven on any city road is an example of a non-uniform motion.
Answer:
The motion of a car moving on a busy road, is non-uniform motion because we have the frequency apply brakes and reduce acceleration on a busy road hence it does not cover equal distance in equal intervals of time.

Question 4.
What do you understand by: a. average speed, b. non-uniform velocity of a body?
Answer:
a. The ratio of the total distance travelled to the total time of travel is called the average speed. It is calculated by ‘ using the formula Total distance travelled

b. If an object covers unequal distances in equal intervals of time in a given direction, it is said to have a non-uniform velocity. If a car moves 70 km in the first hour of its journey and 50 km in the second hour, it is said to have a non-uniform velocity.

Question 5.
Differentiate between mass and weight.
Answer:
Differences between mass and weight –
Mass :

1. The amount of matter contained in a body is called its mass.
2. The mass of a body is constant and does not change with place and position of the body.
3. The mass of a body can never be zero.
4. The SI unit of mass is kilogram (kg).
5. The mass of a body is measured by a simple beam balance or a physical balance.

Weight :

1. The weight of a body is the force with which it is attracted by the earth towards its centre.
2. The weight of a body depends on the force of gravity and thus changes from place to place.
3. The weight of a body can be zero if no force of gravity acts on the body.
4. The SI unit of weight is newton (N).
5. The weight of a body is measured by a spring balance.

F. Solve the following numerical problems.

Question 1.
A man runs around exact half the circumference of a circular park of diameter 40 m. What is the displacement of the man ?
Answer:
The man covers half the circumference of a circular park. This is equal to covering a semi-circle. Therefore, the displacement of the man is equal to the diameter of the park which is 40 m.

Question 2.
An object moves from A to D along a rectangular path as shown in the given figure. Find :
a. the distance covered by the object.
b. the displacement of the object.

Answer:
a. Distance covered by the object = AB + BC + CD
= 10 km + 6 km + 10 km = 26 km
b. Displacement of the object = AD = 6 km

Question 3.
Calculate the speed of an object if it covers 200 metres in 50 seconds.
Answer:
Distance covered (x) = 200 m
Time taken (t) = 50 sec.

= \(\frac {200}{50}\)
= 4 seconds

Question 4.
An express train moves at a speed of 60 km h^-1. How fai* will it travel in 3 hours? ,
Answer:
Speed of train = 60 km hs^-1
Time = 3 hours
Distance = Speed x Time
= 60 x 3 = 180 km

Question 5.
How long will it take for an object moving with a speed of 5 m s^-1 to cover a distance of 20 m?
Answer:
Speed of object = 5 ms^-1
Distance = 20 m

\(\frac {20}{5}\)
= 4 seconds

Question 6.
A train covers a distance of 820 km with a speed of 80 km/hr. How long does it take to finish the journey ?
Answer:
Distance covered (s) = 820 km
Speed (v) = 80 km/hr
Time (t) = ?
We know,

\(\frac {820}{80}\)
= 10.25 hours

Question 7.
A bus moves with an average speed of 60 km/hr for 4.5 hr. Find the distance travelled by it?
Answer:
Speed, v = 60 km/hr
Time (t) = 4.5 hr
Distance (s) = ?

Distance = speed x time = 60 x 4.5 = 270 km

G Identify the types of motions for which the paths are shown below.

Answer:
1. Curvilinear motion.
2. Rolling motion.

H. Interpet the types of motion (uniform or non-uniform) from the information given in the following figures.

Answer:
1. Uniform motion
2. Non Uniform motion

Think And Answer

Question 1.
A man walks at a speed of 1 m/s and covers a certain distance in some time. But, if he walks at a speed of 3 m/s, he covers an additional distance of 15 m in the same time. What is the distance he actually covered?
Answer:
Let the original distance covered be x m.
Time taken to cover rmat the speed of 1 m/s = x seconds
Distance travelled in x s at the speed of 3 m/s = x x 3 = 3x m
According to the question, 3x = x + 15 ⇒ 2x = 15 ⇒ x = 7.5
Hence, the actual distance travelled is 7.5 m.

Question 2.
A child walks 5 m straight from his house, then turns left and walks 12 m. He then walks 13 m straight back to his house. What is his displacement?
Answer:
The displacement of the child will be zero.

Question 3.
Describe the types of motion of a screw when it is turned.
Answer:
A turning screw has both rectilinear and rotatory motions. This is because while it is being rotated (rotatory motion), it is also getting pushed inwards (rectilinear motion) into the material.

Living Science Physics Class 7 ICSE Solutions