Please help.I can't use the law of momentum when the objects are collided.

In summary, the conversation discusses finding the final velocity of a ball when hit by a bat. The solution involves considering the bat's angle, velocity, and grip on the ball. The problem can be simplified to a one-dimensional momentum problem if the bat is moving freely and has no relative velocity parallel to its surface. However, if the bat is not moving freely, the problem becomes more complex and requires finding the velocity of the ball relative to the bat and its components parallel and perpendicular to the surface.
  • #1
rattisuk
2
0

Homework Statement


Now,I am making the real game.The user can control the bat to hit the ball.
Please look at this picture.
attachment.php?attachmentid=22185&stc=1&d=1259686717.png


Assume m2 is the bat and m1 is the ball
The bat has its angle and its velocity vector(x,y).
I want to find final velocity of the ball. I know the vector(x,y) of v1,v2 ,angle of the bat.
I can't use this formula :
m1v1+m2v2 = m1v1f+m2v2f and the formula for the conservation of kinetic energy
(v1f is the final velocity of the ball)
because the picture left and right have the same value of v1,v2.so they will have the same v1f.

Homework Equations


The Attempt at a Solution


I try to find the normal of the bat and calculate it .follow by this picture.
attachment.php?attachmentid=22187&stc=1&d=1259688127.png

Sorry,The Picture is not correct; I use this formula : v1f = vv+v2But it's not good
How can I find the final velocity of the ball?
Please give me some solution.:cry:
 

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  • #2
If the bat is moving freely (nothing holding one end) and the middle of the bat hits the ball, and the bat & ball have no relative velocity in the direction parallel to its surface, then the solution is an easy one dimensional momentum problem, where the only direction that matters is the one perpendicular to the bat. If there is a component of velocity parallel to the bat, then you have to do something with the "grip" or friction between bat and ball to figure out what should happen in that direction. If the grip is strong then the velocities of bat and ball in that direction will become equal while conserving momentum in that direction. Of course if you are considering rotational motion of the ball and/or the bat, then it is more complicated!
If the bat is moving parallel
 
  • #3
If the bat is NOT moving freely, but is just being moved by the hand and it keeps the same velocity during the collision, or if the bat is much heavier than the ball (both of these will be the case with pingpong bats), then it's just the same problem as the ball bouncing from a surface. You can use the equation in your drawing in your solution attempt. You only need to find vv.

You have to find the velocity of the ball relative to the bat, Then find the components of this velocity parallel to and perpendicular to the surface, And then flip the perpendicular component, and finally add the speed of the bat to the ball speed again to get the velocity of the ball relative to the earth.
 
  • #4
Thank you for every solution.
 

FAQ: Please help.I can't use the law of momentum when the objects are collided.

What is the law of momentum?

The law of momentum states that in a closed system, the total momentum before a collision is equal to the total momentum after the collision.

Why can't I use the law of momentum in collisions?

The law of momentum can only be applied in collisions that occur in a closed system, meaning that there are no external forces acting on the objects. If there are external forces, such as friction or air resistance, the law of momentum cannot be applied.

Can the law of momentum be used for all types of collisions?

No, the law of momentum can only be used for collisions that are elastic or completely inelastic. In elastic collisions, kinetic energy is conserved, while in completely inelastic collisions, kinetic energy is not conserved.

What are some real life examples of the law of momentum?

The law of momentum can be seen in many everyday situations, such as a game of pool where the balls collide with each other, or a car crash where the momentum of the two cars is transferred during impact.

How can I solve problems involving the law of momentum?

To solve problems involving the law of momentum, you will need to know the masses and velocities of the objects before and after the collision. You can then use the equation p = mv (momentum = mass x velocity) to calculate the total momentum before and after the collision and determine if it is conserved.

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