GME asked 1 year ago
A crane is used to lower weights into the sea(density = 1025 kg/m^3) for an underwater construction project. Determine the tension in the rope of the crane due to a rectangular 0.4m x 0.4m x 3m concrete block (density = 2300 kg/m^3) when it is completely in the air and completely immersed in water. Answers in kN
1 Answers
Sazid Ahmad answered 1 year ago
The block has a volume of 0.4 * 0.4 * 3 = 0.48 m3
So it has a mass of 2300 * .48 = 1104 kg
Therefore the tension in the rope when it is out of the water is mg
= 1104 * 9.81 = 10830 N = 10.83 kN
In the water, it displaces 0.48 m3 of water which has a mass of 0.48 * 1025 = 492 kg
So the tension in the rope when it is in the water is (mblock-mwater)g
= (1104 – 492) * 9.81 = 6004 N = 6.00 kN
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