Question

The figure below shows an axe which has
a massless handle of length L and a blade
of mass M and radius R. The man slowly
raises the axe from the horizontal position
to the vertical position by rotating it about
its point B. Find the work done by him on
the axe during the process.
(Final
R position)
L
L
R R
B
(Initial
position)​

Answer 1

Answer:

ANSWER

Let the bob of mass m fall through a height h.

According to work-energy theorem, the charge in potential energy of the bob is converted to the kinetic energies of the bob and the flywheel.

Rotational kinetic energy of a flywheel is given by

2

1

Iw

2

=

2

1

2

mr

2

w

2

=

4

mr

2

w

2

Since the string is tied around the flywheel, v of the bob is related to

w of the flywheel by the relation v=wr

mgh=

2

1

mv

2

+

2

1

Iw

2

=

2

1

mw

2

r

2

+

4

mr

2

w

2

=

4

3mw

2

r

2

gh=

4

3w

2

r

2

,w

2

=

3r

2

4gh

w=

r

1

3

4gh