Consider a rod of mass M and length L is free to rotate about an horizontal axis O passing through its center. A particle of mass m falls from point P which is at a height h from Q and collides elastically with rod at a distance 4 L form O . If the rod makes an angle α with horizontal before collision. Then find the angular velocity of rod just after collision.
Details And Assumptions
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Problem is nice but shouldn't it be specified to take g as 10 because i took 9.8 initially and got wrong answer
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Sorry for trouble, i have mentioned it
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Thanks ! also i had a strong feeling from inside to take g as 9.8 because in answer box it was written that decimals ok :)
What is the equation of e
Can u explain the physical meaning of the e equation and how u got there
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The equation of e the the equation for coefficient of restitution (e) = velocity of approach of objects velocity of separation of objects
how did you get initial angular momentum = m ∗ 5 4 v
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sorry its just a typo it should be m × 5 4 v × 4 l .
It is because we need to take component of velocity perpendicular to rod to calculate initial angular momentum.
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Great solution, are you in fiitjee south delhi
i first did by a different method but ended with a wrong answer ,
i'll be glad if u tell my mistake ,first i found the velocity of particle in direction perpendicular to the rod let it be v' ,
v be the initial perpendicular velocity of the particle which is ( 2 g h ) cos 3 7 the net impulse on rod is m(v+v')
Now using angular impulse - momentum theorem 1 2 M l 2 angular velocity = m(v+v') l/4
after solving i get 5.3333
can u tell what is wrong in my approach ?
i firstly didn't feel like conserving momentum as impulse is acting at the point of contact and hinge will also apply an impulse.
@Mark Hennings sir
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Look at my comment...
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which comment sir ?
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@A Former Brilliant Member – Sorry, report.
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@Mark Hennings – When you are using impulses, you are conserving angular momentum, presuming that the particle has perpendicular speed v ′ after the collision. This is right. However, you never say how you calculate v ′ , so I don't know how the second half of your argument goes...
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@Mark Hennings – v' is calculated by usual conservative of momentum and elasticity condition .
Just conserve angular momentum and put the condition of elasticity.
Can you please post the full solution.Thanks
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By conservation of energy and angular momentum I am getting ans as 3. Please explain how to use condition of elasticity. Also I am not able to see the correct ans even after clicking on veiw solution. So pl tell the correct ams
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Let v 0 be the velocity of particle before collision. And ω the angular velocity of road after collision and v x and v y the component of particle just after collision along and perpendicular the rod respectively
From the equation of e along the line of impact:
e = 1 = − 0 − 5 4 × v 0 4 l × ω − v y
→ 4 l × ω − v y = 5 4 × v 0
Now conserving angular momentum form the point where rod is attached to the axis:
m × 5 4 v 0 × 4 l = m v y × 4 l + I ω , where I is the moment of inertia of rod ( I = 1 2 m l 2 )
Now substituting the value of v y we get ω = 6