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

[astru025]

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]

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!

 

[astru025]

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

 

[astru025]

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?!

 

[astru025]

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

 

[Doc Al]

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?

 

[astru025]

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

 

[Doc Al]

Momentum? Law of conservation of mometum?

Exactly.

... I don't have a clue!

Sure you do.

 

[astru025]

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 :)