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Adv Physics

Adv Physics. Chapter 5 Sections 5 and 6. Conservation of Mechanical Energy. If gravity is the only force that does work on an object, the total mechanical energy stays the same ΣE i = ΣE f Mechanical energy --- KE, GPE. Sample Problem.

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Adv Physics

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  1. Adv Physics Chapter 5 Sections 5 and 6

  2. Conservation of Mechanical Energy • If gravity is the only force that does work on an object, the total mechanical energy stays the same ΣEi = ΣEf Mechanical energy --- KE, GPE

  3. Sample Problem A 65 kg diver is poised at the edge of a 10 m platform. Calculate the diver’s gravitational potential energy and kinetic energy at 10 m, 5 m, 2 m, and 0 m above the water’s surface.

  4. Sample Problem An arrow with a mass of 0.05 kg is fired vertically from a height of 5 m above the ground and reaches a height of 51 m. Ignoring air resistance, determine the speed with which it was fired and the speed of the arrow after falling back to a height of 20 m above the ground.

  5. Sample Problem A motorcycle is trying to leap across a canyon by driving horizontally off the cliff. When it leaves the cliff, the cycle has a speed of 55 m/s. Find the speed with which the cycle strikes the ground on the other side. The first cliff is 70 m high and the second is 35 m high.

  6. Sample Problem A skier travels down a 30 degree slope starting with a speed of 5 m/s. If he travels 15 m along the slope to the bottom, find his final velocity.

  7. Power • Average power – rate at which work is done P = W / t where P – power W – work t – time [P] = J/s = Watt, W ft lb/s

  8. Power cont’d. • Horsepower – Watt’s estimate of the maximum average power that a horse could deliver over a work day 1 hp = 746 W = 550 ft lb/s Instantaneous power – power at any instant P = Fv

  9. Sample Problem A woman drives her car up a parking ramp 12 m high at a constant speed in 20 s. The mass of the car is 1500 kg. Calculate the average power output of the car’s engine during this time in horsepower.

  10. Sample Problem A motor driven winch pulls a 50 kg student 5 m up a rope at a constant speed of 1.25 m/s. How much power does the motor use in raising the student? How much work does the motor do on the student?

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