Recitation Worksheet J Solutions

# Recitation Worksheet J Solutions - Worksheet J Conservation...

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Worksheet J: Conservation of energy. 1. A small bead of mass m = 30 g hangs at one end of a string of length l = 10 cm. The other end is attached to the ceiling as shown in the figure below. The bead is pulled up, so the string makes an angle θ 0 = 70 ° with the vertical, and released from there. Air resistance is negligible. a. Is mechanical energy conserved? Why? Yes. The only force doing work is gravity, which is a conservative force. (The tension on the string does zero work because it is always perpendicular to the trajectory). b. Write the potential energy of the bead as a function of . Take the potential energy to be zero at the lowest point of the trajectory. () ( 1 c o s) Um g l =− (for details, see lecture notes) c. Fill in the table below with the appropriate values of the mechanical energy, the potential energy, the kinetic energy and the speed of the bead at different angles. 32 2 (30 10 kg)(9.8 m/s )(10 10 m) 0.0294 J 2.94 mJ ( ) (2.94 mJ)(1 cos ) (70 ) 19 mJ (because the initial kinetic energy is zero) and always has the same value.

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Recitation Worksheet J Solutions - Worksheet J Conservation...

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