Solving Collision and Kinetics Problems in 2D

In summary, the conversation focuses on the topics of collisions in 2D, rotational kinetics, and rotational dynamics. The individual is seeking help with five specific questions related to these concepts and is willing to pay it forward once they have a better understanding. The questions involve determining the speed and direction of objects after collisions, calculating the mass of a cylinder, finding the speed of a block after falling a certain distance, determining the angular acceleration and speed of a rod, and calculating the tension and reaction forces on a beam. The person is reminded to follow forum rules and post each question in a separate thread with relevant equations and their own working.
  • #1
doub
15
0
Hello Everyone,

I am having a heck of a time with collisions in 2D and with rotational kinetics and rotational dynamics. I have posted 5 questions below that I seem to be having the most troubles with. I know it my be a lot to ask but if anyone here can help me to understand how they got to the answers I would be forever greatful, and will pay it forward.

Thanks

1. A 2.0 kg ball moving with a speed of 3.0 m/s hits, elastically, an identical stationary ball as shown. If the first ball moves away with angle 30° to the original path, determine
- the speed of the first ball after the collision.
- the speed and direction of the second ball after the collision.


2. A light string is wrapped around a solid cylinder and a 300 g mass hangs from the free end of the string, as shown. When released, the mass falls a distance 54 cm in 3.0 s.
- Calculate the mass of the cylinder.


3. A solid sphere of mass 6.0 kg is mounted on a vertical axis and can rotate freely without friction. A massless cord is wrapped around the middle of the sphere and passes over a 1.0 kg pulley and is attached to block of mass 4.0 kg, as shown. What is the speed of the block after it has fallen 80 cm? Treat the pulley as solid cylinder.


4. Consider a uniform rod of mass 12 kg and length l.0 m. At its end, the rod is attached to a fixed, friction-free pivot. Initially the rod is balanced vertically above the pivot and begins to fall (from rest) as shown in the diagram. Determine,
the angular acceleration of the rod as it passes through the horizontal at B.
the angular speed of the rod as it passes through the vertical at C.


5. A uniform vertical beam of mass 40 kg is acted on by a horizontal force of 520 N at its top and is held, in the vertical position, by a cable as shown.
Calculate the tension in the cable?
Determine the reaction forces acting on the beam by the ground?
 
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  • #2
Please post each question in a separate thread, provide relevant equations you are aware of and your own working as far as you get - as per forum rules.
With luck, after two or three of the threads have reached a satisfactory conclusion you won't need to post any more.
 

1. What is the difference between elastic and inelastic collisions?

Elastic collisions involve objects that bounce off each other without any energy loss, while inelastic collisions involve objects that stick together or deform upon collision and result in some energy loss.

2. How do you calculate the momentum of an object in 2D?

To calculate the momentum of an object in 2D, you need to know its mass and velocity in both the x and y directions. The momentum in the x direction is calculated by multiplying the mass by the velocity in the x direction, and the momentum in the y direction is calculated by multiplying the mass by the velocity in the y direction. The overall momentum can then be calculated by using the Pythagorean theorem to find the magnitude of the momentum vector.

3. What is the law of conservation of momentum?

The law of conservation of momentum states that in a closed system, the total momentum of all objects before a collision is equal to the total momentum after the collision. This means that the total momentum is conserved and does not change unless an external force acts on the system.

4. Can you solve 2D collision and kinetics problems using only algebra?

Yes, 2D collision and kinetics problems can be solved using only algebra. By using the laws of conservation of momentum and energy, along with basic kinematic equations, you can set up and solve systems of equations to find the unknown variables in a problem.

5. How do you determine the final velocities of objects after a collision in 2D?

To determine the final velocities of objects after a collision in 2D, you need to first analyze the type of collision (elastic or inelastic) and then use the equations for conservation of momentum and energy to set up and solve a system of equations. By solving for the final velocities in each direction, you can determine the overall final velocity of each object.

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