Bar Swinging Up After Collision - Strategy

In summary, a uniform bar is suspended by a frictionless hinge. A horizontally launched blob of clay sticks to the bottom end of the bar, causing it to swing upward. The minimum initial speed of the blob of clay needed for the bar to swing a full circle can be solved using conservation of energy and conservation of angular momentum.
  • #1
postfan
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Homework Statement



A uniform bar of mass m and length l is suspended on a frictionless hinge. A horizontally launched blob of clay of mass m strikes the bottom end of the bar and sticks to it. After that, the bar swings upward. What is the minimum initial speed v of the blob of clay that would enable the rod to swing a full circle?
Which concepts/laws would be most helpful in solving this problem? Select the best answer from the options below.
CHOICES
kinematics of rotational motion; conservation of energy
conservation of momentum, conservation of energy
conservation of angular momentum, conservation of momentum
conservation of angular momentum, conservation of energy
conservation of energy, Newton's laws
Newton's laws, conservation of angular momentum
conservation of angular momentum, kinematics of rotational motion
Newton's laws, kinematics of rotational motion

Homework Equations





The Attempt at a Solution


I though the answer was momentum and linear momentum because the linear momentum converts into the angular one ,but I am wrong. So, what it the right answer?
 
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  • #2
There are multiple ways to solve this, but conserved angular momentum in the collision process is certainly interesting. Linear momentum is not conserved (the hinge can absorb some of the momentum of the clay).
Afterwards, you need some way to find out how high the bar will swing.. what would you use for that?
 
  • #3
Would you use conservation of energy?
 
  • #4
I would use conservation of energy as part of the solution, yes.
 
  • #5
So the answer is conservation of energy and conservation of angular momentum?
 
  • #6
That is probably the answer I would give.
 
  • #7
Ok Thanks!
 

Related to Bar Swinging Up After Collision - Strategy

1. How does the bar swing up after a collision?

The bar swings up after a collision due to the conservation of energy and momentum. When two objects collide, their total energy and momentum remain constant. As the colliding objects exert a force on each other, this force can cause the bar to swing upwards.

2. What is the strategy behind the bar swinging up after a collision?

The strategy behind the bar swinging up after a collision is to manipulate the forces and angles involved in the collision to maximize the upward swing of the bar. This may involve adjusting the mass and velocity of the objects involved or changing the angle of the collision.

3. Can the bar swing up after a collision if the objects have unequal masses?

Yes, the bar can still swing up after a collision if the objects have unequal masses. As long as the total energy and momentum of the system remain constant, the bar will experience an upward swing. However, the magnitude of the swing may differ depending on the masses of the objects involved.

4. How does the angle of the collision affect the bar swinging up after a collision?

The angle of the collision can greatly impact the bar swinging up after a collision. A head-on collision with a 90-degree angle will result in the maximum upward swing of the bar, while a glancing collision with a smaller angle may result in a smaller swing or no swing at all.

5. What other factors besides energy and momentum conservation can affect the bar swinging up after a collision?

Besides energy and momentum conservation, other factors that can affect the bar swinging up after a collision include the elasticity of the objects involved, the presence of external forces, and the shape and material of the bar itself. These factors can alter the amount of energy and momentum transferred during the collision, thus impacting the upward swing of the bar.

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