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: (a) Rope is pulled to draw water from a well. This
changes the state of motion of the water bucket. (b) 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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Chapter-11 Force and Pressure |
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