Kinetic Friction of ride down a ramp

  • Thread starter MarineBio
  • Start date
  • #1
15
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Homework Statement



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?

Homework Equations



mgh

K = 1/2mv^2

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?
 

Answers and Replies

  • #2
turin
Homework Helper
2,323
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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
rock.freak667
Homework Helper
6,230
31

The Attempt at a Solution



initial energy = mgh = 493.92
my calculator does not give that, how did you get that?

But mgh= 1/2mv2 +Wf does look correctly applied.
 
  • #4
15
0
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.
Whoops, silly mistake. You're right, I just had to put a negative sign on the work of friction. Thanks.
 
  • #5
15
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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
jgens
Gold Member
1,581
50
You would need to find the friction force first. You have that Wf = Ff * d and Ff = uk * FN
 

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