Calculating Kinetic Friction on an Amusement Park Ride

[map7s]

A 30.0 kg seal at an amusement park slides down a ramp into the pool below. The top of the ramp is 1.60 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 is done by kinetic friction?
I tried a number of things, but I wasn't sure how to calculate kinetic friction.

 

[OlderDan]

What did you try? This problem is about work and energy. It just happens to be a frictional force doing some work in this problem. All you need to know is the work done by the force, and how that is related to the force and distances involved.

 

[map7s]

I tried doing W=Fdcos(x). I tried that after I did a conservation of energy equation mgh=1/2 mv^2 but I didn't know where to go with that.

 

[OlderDan]

I tried doing W=Fdcos(x). I tried that after I did a conservation of energy equation mgh=1/2 mv^2 but I didn't know where to go with that.

I assume that if you calculated mgh at the top of the slide, and 1/2mv^2 at the bottom you found that mechanical energy was not conserved in this problem. The difference is the work done by friction. Friction acts opposite the direction of motion, so the angle in the dot product is 180 degrees. The work done by friction is negative; it takes mechanical energy from the seal.