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Classical dynamics - rotational motion - Why is there a factor sqrt(2) dofferece between the energy approach and the torque approach?
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1st picture: situation

2nd picture: calculations

A hammer is hanging from a hook (frictionless) and is dropped from a horizontal position so that it swings down to vertically under the hook. The final angular velocity needs to be determined.

This problem can be analysed from the perspective of

conservation of energy. In which case potential energy is

transferred to rotational energy.

It can also be analysed from the perspective of torque. In which case gravity delivers the torque and the torque changes as the angle 8 changes during the fall.

Both are worked out in the second picture with equations 4 and 13 as answers. My question is why there is a factor sqrt(2) difference between the answers? Where did I make a mistake.

(This is for a free project and thus there isn't a answer guide I can refer to.)

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1 year ago