Class 9 Laws of Motion exercise question answer science and technlogoy
Laws of
motion class 9 exercise answers Maharashtra board Laws of motion class 9
solution state board. 9 class science and technology guide pdf Maharashtra
board.
|
Sr. No. |
Column 1 |
Column 2 |
Column 3 |
|
1. |
Negative acceleration |
The velocity of the
object remains constant |
A car, initially at
rest reaches a velocity of 50 km/hr in 10 seconds |
|
2. |
Positive acceleration |
The velocity of the object decreases |
A vehicle is moving with a velocity of 25
m/s |
|
3. |
Zero acceleration |
The velocity of the
object increases |
A vehicle moving with
the velocity of 10 m/s, stops after 5 seconds. |
Answer:
|
Sr. No. |
Column 1 |
Column 2 |
Column 3 |
|
1. |
Negative acceleration |
The velocity of the
object decreases |
A vehicle moving with
the velocity of 10 m/s, stops after 5 seconds. |
|
2. |
Positive acceleration |
The velocity of the object increases |
A car, initially at rest reaches a
velocity of 50 km/hr in 10 seconds |
|
3. |
Zero acceleration |
The velocity of the
object remains constant |
A vehicle is moving
with a velocity of 25 m/s |
2. Clarify the differences
A. Distance and displacement
Answer:
|
Distance |
Displacement |
|
Distance
is the length of the actual path followed by a body between the points under
consideration. |
Displacement is the
shortest distance from the initial point to the final point of movement of a
body. |
|
It
does not have direction. |
It has direction. |
|
It is
greater than or equal to the magnitude of displacement. |
Its magnitude is less
than or equal to the distance. |
B. Uniform and non-uniform motion
Answer:
|
Uniform motion |
Non-uniform motion |
|
A
body is said to have uniform motion when it covers equal distance in very
small equal intervals of time. |
A body is said to have
non-uniform motion when it covers unequal distances in equal intervals of
time. |
|
In
this case, the speed of the body is constant. |
In this case, the speed of the body is
not constant. |
3. Complete the following table.
|
u (m/s) |
a (m/s2) |
t (sec) |
v= u+at (m/s) |
|
2 |
4 |
3 |
14 |
|
10 |
5 |
2 |
20 |
|
u (m/s) |
a (m/s2) |
t (sec) |
s = ut + 1/2at2 (m) |
|
5 |
12 |
3 |
69 |
|
7 |
8 |
4 |
92 |
|
u (m/s) |
a (m/s2) |
s (m) |
v 2 = u2 + 2as (m/s)2 |
|
4 |
3 |
8 |
8 |
|
4 |
5 |
8.4 |
10 |
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4. Complete the sentences and explain them.
a. The
minimum distance between the start and finish points of the motion of an object
is called the ……….. of the object.
Answer:
The minimum distance between the start and finish points of the motion of an
object is called the displacement of the object.
b. Deceleration is ——– acceleration
Answer:
Deceleration is negative acceleration
c. When
an object is in uniform circular motion, its ……… changes at every point.
Answer:
When an object is in uniform circular motion, its velocity changes at every
point.
d.
During collision ……….. remains constant.
Answer:
During collision total momentum remains constant.
e. The
working of a rocket depends on Newton’s ….…. law of motion.
Answer:
The working of a rocket depends on Newton’s third law of motion.
5. Give scientific reasons.
a. When an object falls freely to the ground, its acceleration is uniform.
Answer:
When an
object falls freely, the only force acting of the object is that due to the
earth’s gravity.
Near
the earth’s surface, this force on a given object is practically uniform.
Hence, an object falling freely to the ground has almost a uniform
acceleration.
b. Even though the magnitudes of action force and reaction force are equal and their directions are opposite, their effects do not get cancelled.
Answer:
Action
and reaction forces act on different bodies. Hence, though their magnitudes are
equal and directions are opposite, their effects do not get cancelled.
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c. It is easier to stop a tennis ball as compared to a cricket ball, when both are travelling with the same velocity.
Answer:
The
momentum of a body is the product of its mass and velocity. The mass of a
cricket ball is greater than that of a tennis ball. Hence, if the two balls
have the same velocity, the momentum of the cricket ball will be greater than
that of the tennis ball.
Also a
cricket ball is harder than a tennis ball. Therefore , it is easy to stop a
tennis ball than a cricket ball moving with the same velocity.
d. The velocity of an object at rest is considered to be uniform.
Answer:
The
velocity of an object at rest is always zero.
Thus,
it does not change with time. Hence, it considered to be uniform.
6. Take 5 examples from your surroundings and give explanation based on Newtons laws of motion.
Answer:
1.the motion of earth around the sun.
2. The motion of the moon around the earth.
3. The motion of the electron around the nucleus of the hydrogen atom.
4. the motion of blades of fan (when the speed is not changed)
5. The motion of a communication satellite ( a geostationary satellite used for communication ) around the earth.
7. Solve the following examples.
a) An object moves 18 m in the first 3 s, 22 m in the next 3 s and 14 m in the last 3 s. What is its average speed?
Answer:
b) An object of mass 16 kg is moving with an acceleration of 3 m/s2 . Calculate the applied force. If the same force is applied on an object of mass 24 kg, how much will be the acceleration? (Ans: 48 N, 2 m/s2)
Answer:
c) A bullet having a mass of 10 g and moving with a speed of 1.5 m/s, penetrates a thick wooden plank of mass 900 g. The plank was initially at rest. The bullet gets embedded in the plank and both move together. Determine their velocity. (Ans: 0.15 m/s)
Answer:
d) A person swims 100 m in the first 40 s, 80 m in the next 40 s and 45 m in the last 20 s. What is the average speed? (Ans: 2.25 m/s2 )
Answer:
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