(d) Since gravity acts downward and perpendicular to the tabletop, (e) Reflect: Whenever a force acts perpendicular to the direction of motion, its contribution to the net work is zero. 7.6. Set Up: Use Calculate the work done by each force. In each case, identify the angle In part (d), the net work is the algebraic sum of the work done by each force. Solve: (a) Since the force exerted by the rope and the displacement are in the same direction, and (b) Gravity is downward and the displacement is at above the horizontal, so (c) The normal force n is perpendicular to the surface of the ramp while the displacement is parallel to the surface of the ramp, so and (d) (e) Now and Reflect: In part (b), gravity does negative work since the gravity force acts downward and the carton moves upward. Less work is done by the rope in part (e), but the net work is still positive. 7.7. Set Up: In order to move the crate at constant velocity, the worker must apply a force that equals the force of friction,
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