The work done to pull the sister back on the swing is equal to the increase in potential energy of the sister:

(1)
where m is the sister's mass, g is the gravitational acceleration and

is the increase in altitude of the sister with respect to its initial position.
By calling

the angle of the chain with respect to the vertical, the increase in altitude is given by

(2)
where L is the length of the chain.
Putting (2) inside (1), we find

from which we can find the mass of the sister:
Hi Pupil Here is your answer ::
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1 The shape of the Body
Example : The shape of the ball lying on a floor can be changed by pressing it.
2 Direction of the Body
Example : The direction of motion of moving ball can be changed by hitting it with a bat.
3 The speed of the Body
Example : A ball at rest can be set in motion if force is applied only
4. Size of the Body
Example : The length of a spring tied and on one end can be increased by pulling it.
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Hope this helps .......
Answer:
Because china was in war, and her parents didn't have enough money for to go to school.
Answer:
Helloooo
Sound created in a big hall will persist by repeated reflection from the walls until it is reduced to a value where it is no longer audible. The repeated reflection that results in this persistence of sound is called reverberation. In an auditorium or big hall excessive reverberation is highly undesirable
Explanation:
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