This post provides you a complete solution of Chapter 7 Motion Class 9 for Rajasthan Board of Secondary Education.
This post contains
all the main and important topics which have complete and detailed description.
|
Board |
RBSE |
|
Subject |
Science |
|
Chapter |
Motion |
|
No. of Intext questions |
20 |
|
No. of End exercise questions |
10 |
|
Prescribed Book |
NCERT Science |
Motion Questions- Answers
Intext Questions
Answers of Questions on Page 74
Q.1 An object has moved
through a distance. Can it have zero displacement? If yes, support your answer
with an example.
Answer
Yes, it can have zero displacement as for example, if a
person throws a ball upwards on a height ‘h’ and catch
back it then the
Distance
covered by the ball = h + h = 2h
Displacement of the ball = 0.
Q.2 A farmer moves along the boundary of a square field
of side 10 m in 40 s. What will be the magnitude of
displacement of the farmer at the end of 2 minutes 20
second from
his initial position?
Answer
If the farmer starts from point A, then at the end of 2
min. and 20 sec. (=2 × 60 + 20) = 140. He will reach the
diagonally opposite corner C. The magnitude of
displacement of the farmer is
So, displacement of farmer at the end of 2 min 20 sec
from his initial position is 14.14m.
Answers of Questions on Page 76
Q.1 Distinguish between
speed and velocity.
Answer
Q.2 Under what condition is the magnitude of the
average velocity of an object equals to its
average speed?
Answer
When an object moves in one direction along a straight
line.
Q.3 What does the
odometer of an automobile measure?
Answer
Odometer of an automobile measure distance travelled by
the automobile.
Q.4 What does the path of an object look like when it is
in uniform motion?
Answer
Straight line path.
Q.5 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
Answers of Questions on Page 77
Q.1When will you say a body is in : (i) Uniform
acceleration, (ii) Non-uniform acceleration?
Answer
(i) A body has uniform acceleration if its velocity changes
by an equal amount in equal intervals of time.
(ii) A body has non-uniform acceleration if its velocity
changes by unequal amount in equal interval of time.
Q.2 A bus decreases its speed from 80 kmh-1 to 60
kmh1 in 5 s. Find acceleration of the bus.
Answer
Answers of Questions on Page 81
Q.1 What is the nature
of the distance-time graphs for uniform and non-uniform motion of an object?
Answer
(i) For uniform motion distance-time graph is a straight
line having constant gradient or slope as shown in figure
(ii) For non-uniform motion, distance-time graphs is a
curve having increasing gradient or slope or decreasing
gradient as shown in figures.
Q.2 What can you say about the motion of an object
whose distance-time graph is a straight line parallel to the
time-axis?
Answer
It means the distance of the object is not changing with
time. Thus, the object is stationary.
Q.3 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
The object has a uniform speed.
Q.4 What is the quantity which is measured by the area
occupied below the velocity-time graph?
Ans.
Distance covered by the body in the
given time interval.
OR
Magnitude
of the displacement of a body.
Answers of Questions on Page 82-83
Q.1A bus starting from rest moves with a uniform
acceleration of 0.1 ms-2 for 2 minutes.
Find: (a) the speed
acquired, (b) distance travelled.
Q.2A train is travelling at a speed of 90 kmh-1. Brakes
applied so as to produce a uniform acceleration of – 0.5
ms-1. Find how far the train will go before it is brought to
rest?
Q.3 A trolley, while going down an inclined plane has an
acceleration of 2 cms-2. What will be its velocity 3 s after
the start?
Answer
Q.4 A racing car has a uniform acceleration of 4 ms-2.
What distance will be cover in 10s
after start?
Answer
Q.5 A stone is thrown in a vertically upward direction
with a velocity of 5 ms-1. If the acceleration of the stone
during its motion is 10 ms-2 in the downward direction,
what will be the height attained by the stone and how
much time will it take to reach there.
Answer
Answers of End Exercise Questions on Page
85-86
Q.1 An athlete completes on round of a circular track of
diameter 200 m in 40 s. What will be the distance
covered and the displacement at the end of 2 minutes
and 20 second?
Answer
Q.2 Joseph jogs from one end A to the other end B of a
straight 300 m road in 2 minutes 50 seconds and then
turn around and jogs 100 m back to point C in another 1
minute. What are Joseph’s average speed and velocities
in jogging (a) from A to B and (b) from A to C?
Answer
Q.3 Abdul, while driving to school, computes the average
speed for his trip to be 20 kmh-1. On his return trip along
the same route, there is less traffic and the average speed
is 30 kmh-1. What
is the average speed for Abdul’s trip?
Answer
in a straight line at a constant rate of 3.0 ms-2 for 8.0 s.
How far
does the boat travel during this time?
Answer
Q.5 A driver of a car travelling at 52 kmh-1 applies the
brakes and accelerates uniformly in the opposite
direction. The car stops in 5s. Another driver going at 3
kmh-1 in another car applies his breaks slowly and stop
in 10 s. On the same graph paper the speed versus time
graph for the two cars. Which of the two cars travelled
farther after the brakes were
applied?
Answer
Q.6Figure shows the distance-time graph of three objects
A, B and C. Study the graphs and answer the following
questions:
Answer
(i) Which of the three is travelling the fastest.
(ii) Are all three ever meet at the same point on the road?
(iii) How far has C travelled when B passes A?
(iv) How far has B travelled by the time it passes C?
Answer
Q.7 A ball is gently dropped from a height of 20 m. If its
velocity increases uniformly at the rate of 10 ms-2, with
what velocity will it strike the ground? After what time
will it strike the ground?
Answer
Q.8 The speed-time graph for a car is shown in figure.
(a) Find how far the car travels in the first four seconds.
Shade the area on the graph that represents the distance
travelled by the car during the period.
(b) Which part of the graph represents uniform motion of
the car?
Answer
Q.9 State which of the following situations are possible
and give an example for each of these:
(a)An object with a constant acceleration but zero
velocity.
(b)An object moving in a certain direction with an
acceleration in the perpendicular direction.
Answer
(a) When an object is thrown vertically upwards, it
velocity at the highest point is zero but it has constant
acceleration = 9.8 ms-2.
(b) An object moving in a circular path with uniform
speed its acceleration is always perpendicular to the
direction of the motion of the
object.
Q.10 An artificial satellite is moving in a circular orbit of
radius 42,250 km. Calculate its speed if it takes 24 hours
to revolve around the earth.
Answer
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