law of conservation

Question

A 73.5-kg boy is surfing and catches a wave which gives him an initial speed of 1.60 m/s. He then drops through a height of 1.56 m, and ends with a speed of 8.51 m/s. How much nonconservative work (in kJ) was done on the boy?

 

Answer 1

Hi Femi,

The theoretrical portion of work should correspond to the potential energy lost, i.e. 1.56m*9.8m s^(-2) * mass. Now, v(f)^2 = v(i)^2 + 2ad would correspond to 2*9.8 m s^(-2)*1.56 m + 2.56 m^2 s^(-2) or v(f) = 5.76 m/s. However, he has 8.51 m/s. The kinetic energy difference between these two reflects non-conservative work, I'll leave the further calculations to you.

-- Cheers, --Mr. d.

P.S. I had no idea that surfers got that kind of energy from waves, frankly!