Elastic Collision of a Ball and Block on a Wire

In summary, the ball swings downward and strikes a block initially at rest on a horizontal frictionless surface. The ball and block have masses of 1.6 kg and 2.4 kg, respectively, and the length of the wire is 1.2 m. The ball velocity just before the collision is V= (0.5*2.4+1.6)*1.2 or 3.2 m/s. The ball velocity just after the collision is V= (0.5*1.6+1.6)*1.2 or 2.8 m/s.
  • #1
emmi1987
4
0

Homework Statement


A ball is attached to one end of a wire, the other end being fastened to the ceiling. The wire is held horizontal and the ball is released from rest. It swings downward and strikes a block initially at rest on a horizontal frictionless surface. Air resistance is negligible and the collision is elastic. The masses of the ball and block are, respectively, 1.6 kg and 2.4 kg and the length of the wire is 1.2 m. Find the velocity (magnitude and direction) of the ball just before the collision and just after the collision.

... I don't even know where to start with this one, I can't find anything about radial? (not sure if that's the appropriate term) motion in regards to velocity. Any help would really be appreciated.


Homework Equations





The Attempt at a Solution

 
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  • #2
emmi1987 said:
... I don't even know where to start with this one, I can't find anything about radial? (not sure if that's the appropriate term) motion in regards to velocity. Any help would really be appreciated.

Hi emmi1987! :smile:

Radial is towards/away from the centre.

Tangential is round the circle (and tangential velocity = angular velocity times radius). :wink:

But you don't need either … just use conservation of energy for the first part, and the usual elastic collision equations for the second part. :smile:
 
  • #3
Thanks! I'm golden on the second part.. but for the first part, do i need to find the time it takes for the ball to fall in order to find v? and then use conservation of energy?
 
  • #4
emmi1987 said:
… for the first part, do i need to find the time it takes for the ball to fall in order to find v? and then use conservation of energy?

Hi emmi1987! :smile:

No, the time doesn't matter …

conservation of energy doesn't depend on how you get from state A to state B (state = position + speed), or how long it takes …

KE(A) + PE(A) = KE(B) +PE(B). :smile:
 

1. What is an elastic radial collision?

An elastic radial collision is a type of collision between two objects where the total kinetic energy and momentum are conserved. This means that after the collision, the objects will continue moving in different directions with the same speed and direction as before the collision.

2. What are the characteristics of an elastic radial collision?

The main characteristics of an elastic radial collision are conservation of kinetic energy and momentum, as well as the absence of any energy loss due to friction or deformation of the objects involved.

3. How is the total kinetic energy calculated in an elastic radial collision?

The total kinetic energy in an elastic radial collision is calculated by adding the kinetic energies of the two objects before the collision and after the collision. This is known as the law of conservation of energy.

4. What is the difference between an elastic and inelastic radial collision?

An elastic collision is one where the total kinetic energy and momentum are conserved, while in an inelastic collision, some of the kinetic energy is lost due to deformation or friction. Inelastic collisions also result in a change in the objects' velocities after the collision.

5. How are the velocities of the objects calculated after an elastic radial collision?

The velocities of the objects after an elastic radial collision can be calculated using the law of conservation of momentum. This law states that the total momentum of the objects before the collision is equal to the total momentum after the collision.

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