11. The system shown in the figure consists of a 4.0 kg block sliding on a horizontal table connected by a string of negligible mass run over a pulley with negligible friction to a hanging 10 kg mass. The two objects are released from rest and the string remains taut throughout the motion. We wish to find the speed of the two objects after the hanging mass has fallen by 20 cm. a. Since only differences in potential energy are important, we can set the zero point of potential energy for each object independently. For the sliding block, consider the zero point of potential energy as the height of the table. For the hanging mass, use its initial height. Using this convention, what is the total initial gravitational potential energy of the system? Remember to include the contributions from both objects. b. Using the same convention, what is the total final gravitational potential energy of the system? c. What is the total kinetic energy of the system after the hanging mass has fallen by 20 cm? You may assume that the effects of friction are negligible. d. What is the speed of each object? Remember that the total kinetic energy is the sum of the kinetic energies of each individual object. e. If instead the coefficient of friction between the table and block is ?k = 0.40, what is the speed of each object after the hanging mass has fallen by 20 cm? Worksheet 15: Conservation of Energy PHYS270, Spring 2016
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