Question 1:
Give two examples each of situations
in which you push or pull to change the state of motion of objects.
Answer:
Two examples of push force are as
follows:
(i) A heavy box at rest is pushed to
move it from one room to another. This changes the state of motion of the box.
(ii) A player pushes a football using
his foot. This changes the state of motion of the ball.
Two examples of pull force are as
follows:
(i) Rope is pulled to draw water
from a well. This changes the state of motion of the water bucket.
(ii) A drawer is pulled to open it.
This changes the state of motion of the drawer.
Question 2:
Give two examples of situations in
which applied force causes a change in the shape of an object.
Answer:
Two examples of forces that cause a
change in the shape of an object are as follows:
(i) Squeezing of a plastic bottle
changes the shape of the bottle.
(ii) Deformation of clay by pressing
it between the hands.
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 __either push or pull__ 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:
(a) In squeezing a piece of lemon,
we make use of muscular force to extract its
juice. This muscular force acts on
the lemon. As a result, the shape of the lemon gets changed.
(b) We use our muscular force to
take out paste from a toothpaste tube. The muscular force acts on the
toothpaste tube. As a result, the shape of the tube gets changed.
(c) Here, the suspended load exerts
a force on the spring and pushes the spring downwards. As a result, the spring
gets stretched. Hence, its shape gets changed.
(d) An athlete pushes the ground
with his feet. His feet exert a muscular force on the ground. This allows him
to jump over the bar. As a result, his 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:
When a blacksmith hammers a hot
piece of iron, he uses his muscular force. This muscular force changes the
shape of the iron so that it can be given a desired shape.
Question 7:
An inflated balloon was pressed
against a wall after it has been rubbed with a piece of synthetic cloth. It was
found that the balloon sticks to the wall. What force might be responsible for
the attraction between the balloon and the wall?
Answer:
On rubbing an inflated balloon with
a piece of synthetic cloth, it becomes charged. A charged body attracts an
uncharged body. When this charged balloon is pressed against a wall, it sticks
to the wall. The force acting between the charged balloon and the wall is the
electrostatic force.
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 make use of muscular force to
hold a 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 but opposite in direction. Therefore, the net force on the
bucket is zero. Hence, there is no change in its 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:
The two forces acting on the rocket
are the force of gravity, which pulls the rocket towards the ground, and the
force of friction due to earth’s atmosphere, which opposes its motion.
Question 10:
When we press the bulb of a dropper
with its nozzle kept in water, 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
(a) pressure of water.
(b) gravity of the earth.
(c) shape of rubber bulb
(d) atmospheric pressure
Answer:
(d) The rise of water in the dropper
is due to atmospheric pressure.
The rise of water in a dropper is
due to atmospheric pressure. When all the air escapes from the nozzle, the
atmospheric pressure, which is acting on the water, forces the water to fill
the nozzle of the dropper.
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