# Homework Help: Simple collisions question

1. Jan 12, 2008

### hasnain721

[SOLVED] simple collisions question

1. The problem statement, all variables and given/known data

http://img180.imageshack.us/img180/1253/28157442gm4.jpg [Broken]

2. Relevant equations

√(2gh)

3. The attempt at a solution

a)

Gravitational potential energy = kinetic energy

this gives u

√(2gh)

= 0.815 metres

b)
i)
In a closed system, total momentum is always conserved.

ii)

Momentum before = momentum after

momentum before :
mass X velocity
(80/100) kg X 4 m/s = 0.32kgm/s

momentum after :
mass X velocity
((80/100) X 3) kg X x = 0.32 kgm/s

therefore x = 1.33 m/s

Is that rite?

and for c) :

ah i get it now!!!

Last edited by a moderator: May 3, 2017
2. Jan 12, 2008

### Kurdt

Staff Emeritus
All is fine up to the momentum calculations where you use (80/100) as the mass. This should be (80/1000) or (8/100). You seem to have the right value for the momentum though so thats probably just a typo. What did you get for part c?

EDIT: Just noticed you've solved it.

3. Jan 12, 2008

### hasnain721

oh yes srry! for part c i got : 2.67 seconds is tht rite?

4. Jan 12, 2008

### Kurdt

Staff Emeritus
Looks fine to me.

5. Jan 12, 2008

cheers!