Page 130 - Understanding NCERT Science 09
P. 130
Q uestions Activity ___________ 10.11
1. What is the kinetic energy of an
Lift an object through a certain
•
object?
height. The object can now do work.
It begins to fall when released.
2. Write an expression for the kinetic
This implies that it has acquired some
•
energy of an object.
3. The kinetic energy of an object of
can do more work and hence possesses
mass, m moving with a velocity
more energy.
–1
of 5 m s is 25 J. What will be its energy. If raised to a greater height it
• From where did it get the energy? Think
kinetic energy when its velocity
and discuss.
is doubled? What will be its
kinetic energy when its velocity In the above situations, the energy gets
is increased three times? stored due to the work done on the object.
The energy transferred to an object is stored
10.2.3 POTENTIAL ENERGY as potential energy if it is not used to cause a
change in the velocity or speed of the object.
Activity _____________10.8 You transfer energy when you stretch a
rubber band. The energy transferred to the
• Take a rubber band.
• Hold it at one end and pull from the band is its potential energy. You do work while
other. The band stretches. winding the key of a toy car. The energy
• Release the band at one of the ends. transferred to the spring inside is stored as
• What happens? potential energy. The potential energy
• The band will tend to regain its original possessed by the object is the energy present
length. Obviously the band had in it by virtue of its position or configuration.
acquired energy in its stretched
position. Activity ___________ 10.12
• How did it acquire energy when
stretched? • Take a bamboo stick and make a bow
as shown in Fig. 10.6.
Activity _____________10.9
• Place an arrow made of a light stick on
it with one end supported by the
• Take a slinky as shown below.
• Ask a friend to hold one of its ends. stretched string.
You hold the other end and move away • Now stretch the string and release the
from your friend. Now you release the arrow.
slinky. • Notice the arrow flying off the bow.
Notice the change in the shape of the
bow.
• The potential energy stored in the bow
due to the change of shape is thus used
• What happened? in the form of kinetic energy in
• How did the slinky acquire energy when throwing off the arrow.
stretched?
• Would the slinky acquire energy when
it is compressed?
Activity ___________ 10.10
• Take a toy car. Wind it using its key.
• Place the car on the ground.
• Did it move?
• From where did it acquire energy?
• Does the energy acquired depend on
the number of windings? Fig.10.6: An arrow and the stretched string
• How can you test this? on the bow.
WORK AND ENERGY 119
Rationalised 2023-24
