07_InstSolManual_PDF_Part23

07_InstSolManual_PDF_Part23 - Work and Energy 7-23 7.100....

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7.100. Set Up: For parts (a) and (c), use the energy relation to find the energy in joules and then convert the respective results to food calorie units. Solve: (a) (b) The body’s metabolic processes convert food energy to thermal energy. (c) 7.101. Set Up: The bag has mass Use conservation of energy to calculate the speed of the bag at the top of the cliff: or results in Then analyze the projectile motion of the bag: use the vertical motion equation, to find the time spent in the air; then calculate the horizontal displacement using Solve: Speed: Projectile motion: Reflect: The final speed can also be found using conservation of energy: 7.102. Set Up: Ignore any friction losses in the rope. The 4 kg bucket will rise 2 m above the ground as the 12 kg bucket falls. Note also that the velocity of the buckets must be identical. Conservation of energy, thus becomes: Solve: (a) (b) Reflect: The speed of the buckets would be less than because the potential energy of the buckets would be converted into kinetic energy shared by the mass of the pulley as well as the buckets. 7.103. Set Up:
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