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dashin00 dashin00
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12 years ago
3 friends decide to push their teachers car (900 KG) into an above ground swimming pool. The pools edge is 1.2 meters above the ground. The friends have enough strenght to push with a force of 1,120N. How long must the friends ramp to get the car into the pool? If ou find that friends actually do 18,900 joules of work, what was their efficiency?
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12 years ago
900kg has a weight of g*m = 900 * 9.8 = 8820 newtons.  The hyptotenuse length to height ratio of the ramp is equal the weight of the car over the force applied, 8820 / 1120 = 7.875.  The height is 1.2 meters so the hypotenuse is 7.85 * 1.2 = 9.45 meters.  the horizontal side is found with the pythagorean formula

Sqrt(9.48^2 - 1.2^2) = L = 9.37 meters

The work recieved by the car is the force times the distance, which is the weight of the car times the vertical displacement which is 8820N * 1.2m = 10584 N.  Efficiency is 10584 / 18900 = 56%
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