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

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!!

Doc Al
Mentor
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!

Ahh forgot to change 11 cm to meters. My answer of 1.47 proved to be correct! Thanks so much

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?!

I tried the equation Vf^2= Vi^2 + 2gh but my answer proved incorrect. The answer I calculated was .07 m/s

Doc Al
Mentor
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?

Momentum? Law of conservation of mometum?... I don't have a clue!

Doc Al
Mentor
Momentum? Law of conservation of mometum?
Exactly.

... I don't have a clue!
Sure you do.

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 :)