# Cube sliding down with frictionless slide

1. Oct 31, 2014

### Nikou

1. The problem statement, all variables and given/known data
A cube with m mass is released from the top of a slide, of h height, with a horizontal distance of d.

2. Relevant equations
Assuming there is no friction between the cube and the slide, ¿what is the minimal information i need to calculate the speed of the cube at the end of the slide?

3. The attempt at a solution

I tried to solve it using the conservation of mechanical energy, so:

Initial mechanical energy = mgh
Final mechanical energy = (mv2
Therefore

mgh=(mv2
gh=(v2
2gh=v2
√2gh=v

So i only need to know g and h to solve this but the solution is not that, according to the website where i got this problem. The solution of the problem would be this:

We have this:

v2f=v2i + 2gΔx
(v2i = 0 because at the beginning is static)

Where Δx is the displacement of the cube, therefore

vf=√(2gΔx)

To find the value of Δx we use phytagoras theorem:

Δx=√(d2+h2)

So to calculate vf we need to know d ,h, g

Why this solution is correct ,since mine requires less information?

(Sorry for my English, is not my first language)

2. Oct 31, 2014

### haruspex

The above appears to be taking the acceleration down the slope as g, but it will be less than that.