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Chapter 9
Force and Laws of Motion
Intext Questions
On Page 118
Question 1:Which of the following has more inertia?
(a)A rubber ball and a stone of the same size?
(b)A bicycle and a train?
(c)A five-rupee coin and a one-rupee coin?
Solution:Inertia of an object is the measurement of its mass.
(a) A stone of same size as that of rubber ball will have a greater mass
because the stone will have more inertia.
(b) A train has much greater mass than that of a bicycle, so the train will
have more inertia.
(c) A five-rupee coin has more mass than a one-rupee coin, so five-rupee
coin will have greater inertia.
Question 2:In the following example, try to identify the number of times
the velocity of the ball changes: "A football player kicks a football to
another player of his team who kicks the football towards the goal. The
goalkeeper of the opposite team collects the football and kicks it
towards a player of his own team." Also identify the agent supplying the
force in each case.
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Solution:Given below are the number of times at which the velocity of
the ball changes.Whenever a force will be applied on the ball then the
velocity of the ball will change.
a) When first player kicks the ball towards another player of his team
then the velocity of ball will change because first player applies some
force on the ball.
b) When another player kicks the ball towards the goal, then the velocity
of ball will change, here again the force is applied on the ball.
c) When goalkeeper of the opposite team collects the ball, then the
velocity of ball will change, it becomes zero. Here the goalkeeper applies
some force on the ball to stop.
d) When the goalkeeper kicks the ball towards his own team, the
velocity of the ball changes because goalkeeper applies some force on
the ball.
Question 3:Explain why some of the leaves may get detached from a
tree if we vigorously shake its branch?
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Solution:We know that the leaves are attached to the tree and are in a
state of rest initially. But when the tree is vigoursly shaken, the branches
of the tree comes in the state of motion but the leaves tend to maintain
their state of rest, as a result the leaves get detached from the tree and
fall down.
Question 4:Why do you fall in the forward direction when a moving bus
brakes to a stop and fall backwards when it accelerates from rest?
Solution:Initially when the bus is at rest our body also follows the same
state. But all of a sudden when the bus starts to move the lower part of
our body tends to move with the motion of the bus, but the upper part
rejects this state of motion and continues to be in a state of rest. This
results in a sudden jerk backwards when a bus moves. Also, a person
standing in a bus will be in a state of motion, and when the brakes are
applied the lower part of our body comes to the state of rest but our
upper part is in a state of motion. Hence, we tend to fall forward when
the bus applies brakes.
On Page 126
Question 1:If action is always equal to the reaction, explain how a horse
can pull a cart?
www.ncrtsolutions.in
Chapter 9
Force and Laws of Motion
Intext Questions
On Page 118
Question 1:Which of the following has more inertia?
(a)A rubber ball and a stone of the same size?
(b)A bicycle and a train?
(c)A five-rupee coin and a one-rupee coin?
Solution:Inertia of an object is the measurement of its mass.
(a) A stone of same size as that of rubber ball will have a greater mass
because the stone will have more inertia.
(b) A train has much greater mass than that of a bicycle, so the train will
have more inertia.
(c) A five-rupee coin has more mass than a one-rupee coin, so five-rupee
coin will have greater inertia.
Question 2:In the following example, try to identify the number of times
the velocity of the ball changes: "A football player kicks a football to
another player of his team who kicks the football towards the goal. The
goalkeeper of the opposite team collects the football and kicks it
towards a player of his own team." Also identify the agent supplying the
force in each case.
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,www.ncrtsolutions.in
Solution:Given below are the number of times at which the velocity of
the ball changes.Whenever a force will be applied on the ball then the
velocity of the ball will change.
a) When first player kicks the ball towards another player of his team
then the velocity of ball will change because first player applies some
force on the ball.
b) When another player kicks the ball towards the goal, then the velocity
of ball will change, here again the force is applied on the ball.
c) When goalkeeper of the opposite team collects the ball, then the
velocity of ball will change, it becomes zero. Here the goalkeeper applies
some force on the ball to stop.
d) When the goalkeeper kicks the ball towards his own team, the
velocity of the ball changes because goalkeeper applies some force on
the ball.
Question 3:Explain why some of the leaves may get detached from a
tree if we vigorously shake its branch?
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, www.ncrtsolutions.in
Solution:We know that the leaves are attached to the tree and are in a
state of rest initially. But when the tree is vigoursly shaken, the branches
of the tree comes in the state of motion but the leaves tend to maintain
their state of rest, as a result the leaves get detached from the tree and
fall down.
Question 4:Why do you fall in the forward direction when a moving bus
brakes to a stop and fall backwards when it accelerates from rest?
Solution:Initially when the bus is at rest our body also follows the same
state. But all of a sudden when the bus starts to move the lower part of
our body tends to move with the motion of the bus, but the upper part
rejects this state of motion and continues to be in a state of rest. This
results in a sudden jerk backwards when a bus moves. Also, a person
standing in a bus will be in a state of motion, and when the brakes are
applied the lower part of our body comes to the state of rest but our
upper part is in a state of motion. Hence, we tend to fall forward when
the bus applies brakes.
On Page 126
Question 1:If action is always equal to the reaction, explain how a horse
can pull a cart?
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