# Kinetic Friction of ride down a ramp

1. Jul 23, 2009

### MarineBio

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

A 28.0 kg seal at an amusement park slides down a ramp into the pool below. The top of the ramp is 1.80 m higher than the surface of the water and the ramp is inclined at an angle of 30.0° above the horizontal. The seal reaches the water with a speed of 4.90 m/s.

What is the work done by kinetic friction?

2. Relevant equations

mgh

K = 1/2mv^2

3. The attempt at a solution

initial energy = mgh = 493.92

final energy = Kf = 1/2mv^2 = 336.14

If the initial was 493.92 and the final was 336.14 then I would assume there was a loss of 157.78, but that wasn't the right answer. Any help?

2. Jul 23, 2009

### turin

I believe that you did this problem correctly. The only two things that I can think of are significant figures and minus sign conventions. I would call the work negative.

3. Jul 23, 2009

### rock.freak667

my calculator does not give that, how did you get that?

But mgh= 1/2mv2 +Wf does look correctly applied.

4. Jul 23, 2009

### MarineBio

Whoops, silly mistake. You're right, I just had to put a negative sign on the work of friction. Thanks.

5. Jul 23, 2009

### MarineBio

Ok so the answer was -157.78 J and in order to find the coefficient of kinetic friction, uk, I thought it would be to simply divide by (mg) but I guess it isn't that simple in this scenario. How would I determine uk?

6. Jul 23, 2009

### jgens

You would need to find the friction force first. You have that Wf = Ff * d and Ff = uk * FN