Two spheres of the same size are connected with a long, massless cord and sink down in water with a constant speed v. When the string is cut, the upper sphere rises back up with the same constant velocity v. The lower sphere consists of aluminum with a density of ρAl = 2700 kg m−3. You can assume the value ρwater = 1000 kg m−3 for the density of water. Determine the density ρ of the upper sphere.
 Provide your reponse without using the word ρal.
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