1)
Give two examples each of situations in which you push or pull to change the
state of motion of objects.
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:
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.
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.
his foot. This changes the state of motion of the ball.
2)
Give two examples of situations in which applied force causes a change in the
shape of an object.
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:
change in the shape of an object are as follows:
(i) Squeezing of a plastic bottle
changes the shape of the bottle.
changes the shape of the bottle.
(ii) Deformation of clay by pressing
it between the hands.
it between the hands.
3)
Fill in the blanks in the following statements.
Fill in the blanks in the following statements.
(a) To draw water from a well we have
to __pull__ at the rope.
to __pull__ at the rope.
(b) A charged body __attracts__ an
uncharged body towards it.
uncharged body towards it.
(c) To move a loaded trolley we have
to __either push or pull__ it.
to __either push or pull__ it.
(d) The north pole of a magnet
__repels__ the north pole of another magnet.
__repels__ the north pole of another magnet.
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
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
ANSWER:-
(a) To stretch the bow, the archer
applies a force that causes a change in its __shape__.
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.
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.
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.
target, the forces acting on it are due to __gravity__ and that due to
__friction__ of air.
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.
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.
Squeezing a piece of lemon between the fingers to extract its juice.
(b)
Taking out paste from a toothpaste tube.
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.
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.
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.
piece of lemon, we make use of muscular force to extract its juice. This
muscular force acts on the lemon.
b) We use our muscular force to take
out paste from a toothpaste tube. The muscular force acts on the toothpaste
tube.
out paste from a toothpaste tube. The muscular force acts on the toothpaste
tube.
(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.
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.
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.
As a result, his state of motion gets changed.
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?
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.
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.
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?
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
Pressure of water.
(b)
Gravity of the earth.
Gravity of the earth.
(c)
Shape of rubber bulb
Shape of rubber bulb
(d)
Atmospheric pressure
Atmospheric pressure
ANSWER :-( d) atmospheric
pressure
pressure