NCERT Solution
Force and Pressure Chap 8 for class 8
Click the below links
to know more……
|
REPRODUCTION IN ANIMALS NIMALS
Chap 6 |
Exercises
Question 1
Give two examples each of
situations in which you push or pull to change the state of motion of objects.
Answer
(a) Pull situations (in which state
of motion of objects is changed):
1. Moving a book placed on a table towards ourselves to read.
2. We pull the clothes out of the washing machine after they are
clean.
(b) Push situations (in which the state
of motion of objects is changed):
1. A football player taking a penalty kick, hits (or pushes) the
ball towards the goal.
2. A cricket ball hit by a batsman.
Question 2
Give two examples of situations in
which applied force causes a change in the shape of an object.
Answer
1. When we press a lump of dough kept on a plate with our hands,
its shape changes.
2. When we press a smiley ball, its shape changes.
Question 3
Fill in the blanks in the following
statements.
(a) To draw water from a well, we
have to ............... at the rope.
(b) A charged body ...............
an uncharged body towards it.
(c) To move a loaded trolley, we
have to ............... it.
(d) The north pole of a magnet
............... the north pole of another magnet.
Answer
(a) To draw water from a well, we
have to pull at the rope.
(b) A charged body attracts an
uncharged body towards it.
(c) To move a loaded trolley, we
have to pull or push it.
(d) The north pole of a
magnet repels the north pole of another magnet.
Question 4
An archer stretches her bow while
taking aim at the target. She then releases the arrow, which begins to move
towards the target. Based on this information, fill up the gaps in the
following statements using the following terms.
muscular, contact, non-contact,
gravity, friction, shape, attraction
(a) To stretch the bow, the archer
applies a force that causes a change in its ...............
(b) The force applied by the archer
to stretch the bow is an example of ............... force.
(c) The type of force responsible
for a change in the state of motion of the arrow is an example of a
............... force.
(d) While the arrow moves towards
its target, the forces acting on it are due to ............... and that due to
............... of air
Answer
(a) To stretch the bow, the archer
applies a force that causes a change in its shape.
(b) The force applied by the archer
to stretch the bow is an example of muscular force.
(c) The type of force responsible
for a change in the state of motion of the arrow is an example of a contact force.
(d) While the arrow moves towards
its target, the forces acting on it are due to gravity and
that due to friction of air.
Question 5
In the following situations,
identify the agent exerting the force and the object on which it acts. State
the effect of the force in each case.
(a) Squeezing a piece of lemon
between the fingers to extract its juice.
(b) Taking out paste from a
toothpaste tube.
(c) A load suspended from a spring
while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump
to clear the bar at a certain height.
Answer
|
S. |
Agent |
Object |
Effect |
Reason |
|
a. |
Fingers |
Lemon |
Shape of
lemon changes |
Muscular
force is exerted on the lemon in order to extract its juice. As a result, the
shape of the lemon changes. |
|
b. |
Fingers |
Tooth
paste tube |
Shape of
tooth paste tube changes |
Muscular
force is exerted on the tube in order to take out paste. As a result, the
shape of the tube changes. |
|
c. |
Suspended
load |
Spring |
The
spring gets stretched. |
The
suspended load pushes the spring downwards. Hence, its shape changes. |
|
d. |
Athlete |
Ground |
Pushes
the ground backwards and as a result takes a high jump to clear the bar at a
certain height. |
When the
athlete pushes the ground with his feet, his feet exert a muscular force on
the ground. Same magnitude of force is applied back by the ground on the
athlete. This force allows them to jump over the bar. As a result, their
state of motion gets changed. |
Question 6
A blacksmith hammers a hot piece of
iron while making a tool. How does the force due to hammering affect the piece
of iron?
Answer
The muscular force applied by the
blacksmith on the hot piece of iron changes the shape of the iron and hence, it
can be moulded in any desired shape.
Question 7
An inflated balloon was pressed
against a wall after it had been rubbed with a piece of synthetic cloth. It was
found that the balloon stuck to the wall. What force might be responsible for
the attraction between the balloon and the wall?
Answer
An electrostatic charge develops on
the balloon after it has been rubbed with a synthetic cloth. Due to this charge
the balloon sticks to the wall. The electrostatic force is responsible for the
attraction between the balloon and the wall.
Question 8
Name the forces acting on a plastic
bucket containing water held above ground level in your hand. Discuss why the
forces acting on the bucket do not bring a change in its state of motion.
Answer
We use muscular force in order to
hold the bucket of water above the ground. This muscular force acts against the
force of gravity that pulls the bucket towards the ground. The two forces are
equal in magnitude and opposite in direction. As a result, the net force on the
bucket is zero. Hence, there is no change in the state of motion.
Question 9
A rocket has been fired upwards to
launch a satellite in its orbit. Name the two forces acting on the rocket
immediately after leaving the launching pad.
Answer
When a rocket has been fired
upwards to launch a satellite in its orbit, two forces acting on it are:
1. Force of gravity acting downwards
2. Frictional force due to the earth's atmosphere, which opposes
its motion.
Question 10
When we press the bulb of a dropper
with its nozzle kept in water, the air in the dropper is seen to escape in the
form of bubbles. Once we release the pressure on the bulb, water gets filled in
the dropper. The rise of water in the dropper is due to
1. pressure of water
2. gravity of the earth
3. shape of rubber bulb
4. atmospheric pressure
Answer
atmospheric pressure
Reason —
When all the air escapes from the nozzle, a low pressure develops inside the
tube. Due to this the atmospheric pressure, acting on water becomes more than
the pressure inside the tube. As water moves from a higher pressure area to a
lower pressure area, hence on releasing the bulb, water gets filled in the
dropper.
=================================
Don’t forget to share,
like and comment
=================================
No comments:
Post a Comment