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Question

A boy is sitting on a swing at a maximum height of 5m above the ground. When the swing passes through the mean position which is 2m above the ground, its velocity is approximately:

A
7.6 m/s
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B
9.8 m/s
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C
6.26 m/s
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D
None of these
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Solution

The correct option is B 7.6 m/s


The law of conservation of energy states that the total amount of
energy in
an isolated system remains constant over time.
At a maximum height:

K0=0

P0=m×g×H

K1=m×V22

P1=m×g×h

K0+P0=K1+P1

m×g×H=m×V22+m×ghg×H

=V22+g×h

V22=g×Hg×h

V=(2×g×(Hh))

V=(2×9.81×(52))=7.67ms


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