1. Batman (m = 90.0 kg) falls down from an unknown height and lands on the end o
ID: 1262168 • Letter: 1
Question
1. Batman (m = 90.0 kg) falls down from an unknown height and lands on the end of 6.0m long horizontal pice of wood that can rotate around horizontal axis trough the middle of the wooden pice.
a) The angular velocity of the batman just after it lands on the end of the wood si 0.65 rad/s. From what height did he fall? The mass of the wooden pice is 120 kg and its moment of inertia is 1/12ML2.
b) Now the wodden pice osciliates with the batman on the end in vertical position. Whit how much force does he need to hold on the wooden pice when it goes trough vertical.
Explanation / Answer
1)
according to conservation of energy
potential energy is converted into rotational kinetic energy
mgH=0.5Iw2
moment of inertia of wooden piece
=1/12 ML2
BUT when batman falls on wooden piece
=(90+120)*36/12
=630kg-m2
mgH=0.5Iw2
90*9.8H=0.5*630*0.652
H=0.15m
2)
TORQUE=IW
F*L=630*0.65
F=68.25N
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