# Homework Help: Energy conservation

1. Dec 8, 2007

### domagoj412

Hello,
I have one problem...

In what initial speed must barmen throw beer mug on the table so it can travel 2 meters. Mass of the beer mug is 0,3 kg. Sliding loss factor between table and beer mug is 0,3.

I hope you have understand the question, because I am translating it from my mother language and some of terms are new to me...

I have to solve this problem using energy conservation principle.

So kinetic energy is wasted on (abrasion, attrition, friction, rub, Sliding loss - which is the right term):
Ek=W
W is F*s
F is m*g*u

It now becomes:

1/2*m*v^2=m*g*u

This can't be right... Mass is relevant here but with this equation it is equation abridged...

2. Dec 8, 2007

### Shooting Star

I'm not quite sure what exactly you mean by "sliding loss factor". If it is just the co-efficient of kinetic friction, then the result is independent of m. The initial speed would be 3.43 m/s.

If that is the case, then ma = -0.3*mg and v^2 = -2ax, giving the value of v.

If it means something else, please let us know.

3. Dec 8, 2007

### domagoj412

I looked up for the right term, yes I thought on Coefficient of friction which is 0,3.

But i need solve this with energy conversation...

4. Dec 8, 2007

### Shooting Star

Equate work done by frictional force to initial KE.

5. Dec 8, 2007

### domagoj412

When you solve this

Kinetic energy = frictional force * x
Ek=F*x

You get 1,71 m/s

So which is correct?

1,71 or 3,43 m/s?

6. Dec 8, 2007