Reflect: Check the answer by converting it to inches: Since a person’s foot is roughly 6 to 12 inches in length, this result is very reasonable. 7.23. Set Up: Use and The skier stops, so Solve: (a) Setting the two expression for net work equal, Solving for the coefficient of kinetic friction, (b) The mass m of the skier divides out and is independent of m . If is doubled while s is constant then increases by a factor of 4; Reflect: To stop the skier friction does negative work that is equal in magnitude to the initial kinetic energy of the skier. 7.24. Set Up: Do unit conversions. In part (c), Solve: (a) (b) (c) (d) The energy required is 4.186 J. and 7.25. Set Up: Use in part (a) and in part (b). Solve: (a) (b) 7.26. Set Up: Use in parts (a) and (c) and in part (b). Solve: (a) (b) so (c) Since doubling the force results in doubling the length of stretch giving The new length will therefore be 7.27. Set Up: Solve for x to determine the length of stretch and use to assess the corresponding work.
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