Finding velocity after collision if you know mass and height. Help

In summary, the conversation discusses finding the velocity after a collision between a 50 gram ball and a 200 gram pendulum that swings up to a height of 11 cm. The equation Vf= square root of 2gh is used to calculate the velocity, but the initial attempt resulted in an incorrect answer. After correcting for units, the correct velocity of 1.47 m/s is found. The conversation then shifts to finding the initial velocity of the ball before the collision, and it is determined that momentum is conserved during the collision. The final equation used is Vf= M1 x Vi / M1 + M2, resulting in a correct answer of 7.35 m/s.
  • #1
astru025
163
0
Finding velocity after collision if you know mass and height. Help!

Homework Statement



A 50 gram ball enters a a pendulum with mass 200 g. The pair then swings up to a height of 11 cm.
find the velocity immediately after the collision? Then find initial velocity of ball before collision.

Homework Equations


Vf= square root of 2gh.



The Attempt at a Solution


Used above equation and got 14.7 which proved incorrect. Any help would be nice! Thanks!
 
Physics news on Phys.org
  • #2
astru025 said:
Used above equation and got 14.7 which proved incorrect.
You're off by a factor of 10, so I suspect a problem with units. Try again!
 
  • #3
Ahh forgot to change 11 cm to meters. My answer of 1.47 proved to be correct! Thanks so much
 
  • #4
So I have 1.47 m/s for my velocity after the collision. How do I find initial velocity of just the ball right before the collision?!
 
  • #5
I tried the equation Vf^2= Vi^2 + 2gh but my answer proved incorrect. The answer I calculated was .07 m/s
 
  • #6
astru025 said:
So I have 1.47 m/s for my velocity after the collision. How do I find initial velocity of just the ball right before the collision?!
What's conserved during the collision?
 
  • #7
Momentum? Law of conservation of mometum?... I don't have a clue!
 
  • #8
astru025 said:
Momentum? Law of conservation of mometum?
Exactly.

... I don't have a clue!
Sure you do. :wink:
 
  • #9
I used the equation Vf= M1 x Vi / M1 + M2
1.47 = .05 kg x Vi / .05 + .2 = 7.35.
My answer was correct! Thanks so much :)
 

1. How do you calculate velocity after a collision if you know the mass and height?

To find the velocity after a collision if you know the mass and height, you can use the equation V = √(2gh), where V is the velocity, g is the acceleration due to gravity, and h is the height of the object.

2. What units should be used for mass and height in the velocity equation?

For the velocity equation V = √(2gh), the mass should be in kilograms (kg) and the height should be in meters (m).

3. Can this equation be used for all types of collisions?

No, this equation can only be used for collisions where the object is dropped from a height and experiences a change in gravitational potential energy. It cannot be used for elastic collisions.

4. Is there a specific direction for the velocity after a collision?

The direction of the velocity after a collision will depend on the direction of the initial velocity and the direction of the gravitational force. If the object is dropped from a height, the velocity after the collision will be downwards.

5. How accurate is this equation in determining the velocity after a collision?

The velocity equation V = √(2gh) is a simplified equation that does not account for all factors, such as air resistance. Therefore, the calculated velocity may not be entirely accurate but can provide a reasonable estimate.

Similar threads

  • Introductory Physics Homework Help
Replies
20
Views
843
  • Introductory Physics Homework Help
Replies
3
Views
875
  • Introductory Physics Homework Help
Replies
34
Views
555
  • Introductory Physics Homework Help
Replies
5
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
796
  • Introductory Physics Homework Help
Replies
6
Views
2K
  • Introductory Physics Homework Help
Replies
10
Views
2K
  • Introductory Physics Homework Help
Replies
7
Views
4K
  • Introductory Physics Homework Help
Replies
8
Views
5K
  • Introductory Physics Homework Help
Replies
5
Views
2K
Back
Top