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Laparoscopy is a minimally invasive surgical procedure where small surgical instruments are inserted into the body through cannulas (hollow tubes 0.5 to 1.0 cm in diameter) . A cannula is inserted into the skin while sleeved around a trocar (Figure 1) . The skin incision can be made directly with a sharp-tipped trocar as it is being inserted with the cannula. If a blunt-tipped trocar is used, the incision is made beforehand with a surgical blade. After insertion, the trocar is removed, leaving the cannula as an access point for laparoscopic procedures.
Figure 1 Cannula, trocar, and two types of tipsLow-friction trocars increase surgical precision and reduce postoperative scarring. Friction between the skin and trocar tip is tested with synthetic skin and a stationary ramp whose surface is made of the same material as the trocar. For testing, the synthetic skin is pressed against the ramp's surface by a load, weighted to allow the skin to slide down at a constant speed (Figure 2) . In this setup, the weight of the synthetic skin layer is negligible.
Figure 2 Experimental setup to test the friction between trocar and skin
Adapted from W. Firme-Gustavo et al., (C) 2015 Society of Laparoendoscopic Surgeons.
-Which of the following expressions gives the magnitude of the work done by the frictional force F if the synthetic skin slides down the entire length L of the ramp and then is pushed back up to its original position?

Question

Passage
Laparoscopy is a minimally invasive surgical procedure where small surgical instruments are inserted into the body through cannulas (hollow tubes 0.5 to 1.0 cm in diameter) . A cannula is inserted into the skin while sleeved around a trocar (Figure 1) . The skin incision can be made directly with a sharp-tipped trocar as it is being inserted with the cannula. If a blunt-tipped trocar is used, the incision is made beforehand with a surgical blade. After insertion, the trocar is removed, leaving the cannula as an access point for laparoscopic procedures.

Figure 1 Cannula, trocar, and two types of tipsLow-friction trocars increase surgical precision and reduce postoperative scarring. Friction between the skin and trocar tip is tested with synthetic skin and a stationary ramp whose surface is made of the same material as the trocar. For testing, the synthetic skin is pressed against the ramp's surface by a load, weighted to allow the skin to slide down at a constant speed (Figure 2) . In this setup, the weight of the synthetic skin layer is negligible.

Figure 2 Experimental setup to test the friction between trocar and skin
Adapted from W. Firme-Gustavo et al., (C) 2015 Society of Laparoendoscopic Surgeons.
-Which of the following expressions gives the magnitude of the work done by the frictional force F if the synthetic skin slides down the entire length L of the ramp and then is pushed back up to its original position?

Quizplus · Accepted Answer

11ecba2d_12f1_6fa1_a3bf_a1e9c57f7f8b_MD0008_00 Friction is the force that resists sliding between two surfaces, and it is a nonconservative force. A nonconservative force does not conserve the total mechanical energy (potential plus kinetic) in a system. The work done by friction is dissipated as other forms of energy, such as heat and sound. The work W done by a force F applied over a distance or displacement d is: W = Fd The magnitude of the work done by a nonconservative force depends on the total distance through which the force is applied. Friction works against the sliding motion of the load as it slides down the ramp a distance L and back up the ramp a distance L for a total distance of 2L (Choices B and D). Therefore, the expression that gives the magnitude of work done by friction is: W = (F)(2L) (Choice A) The work done by a conservative force (eg, gravity, electrostatic) depends on the net displacement (not distance) the force is applied. Because there is no net displacement in this case, the work done by a conservative force would be zero. However, friction is not a conservative force. Educational objective: Friction is a nonconservative force, which does not conserve the total mechanical energy (potential plus kinetic) in a system. The magnitude of the work W done by a nonconservative force depends on the total distance d through which the force F is applied: W = Fd.

Passage Laparoscopy Is a Minimally Invasive Surgical Procedure Where Small Surgical