Anna R.

asked • 03/26/13

Physcis question

Catching a wave, 77-kg surfer starts with a speed of 1.3 m/s, drops a height of 1.65m, and ends with a speed of 8.2 m/s.  How much non conservative work was done on the suffer?

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Inactive Tutor answered • 03/26/13

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The initial energy (E in) of the surfer includes its initial kinetic energy plus potential energy for the height h =1.65 m. Let's put

            v1 = 1.3 m/s (initial speed),        m = 77 kg,         g = 9.81 m/s^2 (acceleration due to gravity).

Then  E in = mv1^2/2 + mgh = 1311.43 J (rounded to the nearest hundreds).

Its final energy is equal to its kinetic eenrgy with the speed v2 = 8.2 m/s. The energy equals

                                             mv2^2/2 = 2588.74 J

The difference between these two equals to the work done on the surfer which includes work of forces f friction between the surfer and the water (viscosity), and push of the wave. The difference is  1277.31 J.

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