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Please explain this question. I tried it many times but failed.I don't understand the meaning of normal reaction on hinge meaning here.I asked it previously also but got wrong answer .Plss.....help me out in this. Q-A uniform rod of length L and mass M is held horizontally with the help of one light vertical string and a hinge as shown.If the string is cut suddenly,find out the initial normal reaction on the hinge Correct answer is Mg/4(This anwer is correct.Please help me.)

Please explain this question. I tried it many times but failed.I don't understand the meaning of normal reaction on hinge meaning here.I asked it previously also but got wrong answer .Plss.....help me out in this.
Q-A uniform rod of length L and mass M is held horizontally with the help of one light vertical string and a hinge as shown.If the string is cut suddenly,find out the initial normal reaction on the hinge
Correct answer is Mg/4(This anwer is correct.Please help me.)

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Grade:12th pass

2 Answers

Arun
25750 Points
5 years ago
 
take the center of mass as axis of rotation,
the net torque is zero in initial state.
Ta=Tb =>Fa×ra=Fb×rb
here Ta is torque by hinge and Tb is torque by the rope.
ra=rb because the axis of rotation is at the center of the rod.
from this we get our both the forces to be equal.
and the net forces are zero
the forces upward i.e.Fa and Fb are opposed by a force downwards
the only force downwards is mg
Fa +Fb=mg
2Fa=mg   …......from our calculation above.
Fa=mg/2
after cutting the rope the force on right is removed but force on ,left acts as normal reaction and this is equal to mg/2.
Kaushki
19 Points
5 years ago
Thank you so much.Now ,I understand it properly.
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