Conservation of Momentum in Collision between a Ball and a Truck

  • Thread starter cixelsyD
  • Start date
  • Tags
    Momentum
In summary, the conversation discusses a collision between a 0.2kg ball traveling at 20ms-1 to the left and a 20,000kg truck traveling at 25ms-1 to the right. The question asks for the speed of the ball after the collision. The answer is 70ms-1, assuming a completely elastic collision and the coefficient of restitution being 1. The concept of momentum conservation and the use of the reference frame of the truck to solve for the resultant velocity of the ball is also mentioned.
  • #1
cixelsyD
2
0
A ball weighing .2kg is traveling 20ms-1 to the left, a 20 000kg truck is traveling 25ms-1 to the right. What is the speed of the ball after the collision
(M1V1) + (M2V2)before=(M1V1) + (M2V2)after
This seemed so obvious, but i keep getting it wrong. The answer is 70ms-1. The only thing that i could be doing wrong is assuming the change in speed of the truck is negligible. Thanks for the help in advance.
 
Physics news on Phys.org
  • #2
The question is quite unclear.They are implying a completely elastic collision here as the theoretical maximum velocity of ball is 70 m/s,assuming there is no change in velocity of the truck.
Your basic assumption was correct but the manner of application was wrong.If there is no change in momentum of truck then no change in momentum of ball too,isn't it? Then the ball would probably go through the truck! Hence momentum conservation is not justified.
In such cases the coefficient of restitution is defined (which is arbitratily 1 in this case).
 
  • #3
Try looking at this situation from the reference frame of the truck, who's mass is >> than the balls. Then, knowing that kinetic energy is conserved, you can solve for the resultant velocity of the ball treating the mass of the truck as infinitely large. This will yield a very good approximation.
 

1. What is momentum before and after?

Momentum before and after refers to the measure of an object's mass and velocity before and after a collision or interaction with another object. It is a property of moving objects that is conserved in a closed system.

2. How is momentum calculated?

Momentum is calculated by multiplying an object's mass (m) by its velocity (v). The formula for momentum is p = m * v.

3. Is momentum conserved before and after a collision?

In an isolated system, momentum is conserved before and after a collision. This means that the total momentum of the objects involved in the collision remains the same.

4. What happens to momentum if the mass or velocity changes before and after a collision?

If the mass or velocity of an object changes before and after a collision, the momentum will also change. However, in an isolated system, the total momentum will remain the same.

5. How does momentum affect the outcome of a collision?

The conservation of momentum can help predict the outcome of a collision. If the total momentum before and after the collision is the same, the objects will bounce off each other with equal and opposite velocities. If the momentum is not conserved, the objects will stick together or one object will continue to move while the other comes to a stop.

Similar threads

  • Introductory Physics Homework Help
Replies
10
Views
1K
  • Introductory Physics Homework Help
Replies
6
Views
587
  • Introductory Physics Homework Help
Replies
6
Views
1K
  • Introductory Physics Homework Help
Replies
4
Views
1K
  • Introductory Physics Homework Help
Replies
10
Views
1K
  • Introductory Physics Homework Help
Replies
9
Views
2K
  • Introductory Physics Homework Help
Replies
20
Views
842
  • Introductory Physics Homework Help
Replies
10
Views
2K
  • Introductory Physics Homework Help
Replies
15
Views
1K
  • Introductory Physics Homework Help
Replies
4
Views
950
Back
Top