Some engineers have developed a device that provides lighting to rural areas with no access to grid electricity. The device is i
ntended for indoor use. It is driven by gravity, and it works as follows: A bag of rock or sand is raised by human power to a higher location. As the bag descends very slowly, it powers a sprocket-wheel which also rotates slowly. A gear train mechanism converts this slow motion to high speed, which drives a DC generator. The electric output from the generator is used to power an LED bulb. Consider a gravity-driven LED bulb that provides 16 lumens of lighting. The device uses a 10-kg sandbag that is raised by human power to a 2-m height. For continuous lighting, the bag needs to be raised every 20 minutes. Using an efficacy of 150 lumens per watt for the LED bulb, determine (a) the velocity of the sandbag as it descends and (b) the overall efficiency of the device.
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Answer:
The settlement that is expected is 1.043 meters.
Explanation:
Since the pre-consolidation stress of the layer is equal to the effective stress hence we conclude that the soil is normally consolidated soil
The settlement due to increase in the effective stress of a normally consolidated soil mass is given by the formula
where
'H' is the initial depth of the layer
is the Compression index
is the inital void ratio
is the initial effective stress at the depth
is the change in the effective stress at the given depth
Applying the given values we get