Question

A 74-kg boy is surfing and catches a wave which gives him an initial speed of 1.6 m/s. He then drops through a height of 1.56 m, and ends with a speed of 8.5 m/s. How much nonconservative work (in kJ) was done on the boy?

Answer 1

Answer:

Work done, W = 1.44 kJ

Explanation:

Given that,

Mass of boy, m = 74 kg

Initial speed of boy, u = 1.6 m/s

The boy then drops through a height of 1.56 m

Final speed of boy, v = 8.5 m/s

To find,

Non-conservative work was done on the boy.

Solution,

The work done by the non conservative forces is equal to the sum of total change in kinetic energy and total change in potential energy.

$W=\dfrac{1}{2}m(v^2-u^2)+(0-mgh)$

$W=\dfrac{1}{2}m(v^2-u^2)-mgh$

$W=\dfrac{1}{2}\times 74\times (8.5^2-1.6^2)-74\times 9.8\times 1.56$

W = 1447.21 Joules

or

W = 1.44 kJ

Therefore, the non conservative work done on the boy is 1.44 kJ.