Posted by lisa on Tuesday, November 27, 2012 at 1:43pm.
A box with a volume V = 0.03 m^3 lies at the bottom of a lake whose water has a density of 103 kg/m^3.
(a) How much force is required to lift the box, if the mass of the box is 100 kg?
(b) How much force is required to lift the box, if the mass of the box is 70 kg?

physics  drwls, Tuesday, November 27, 2012 at 1:55pm
Check your density of water again.
103 kg/m^3 is much too low.

physics  lisa, Tuesday, November 27, 2012 at 2:02pm
ah thanks, it's 10^3 kg/m^3

physics  drwls, Tuesday, November 27, 2012 at 2:11pm
(a) The buoyancy force on the box is
V*(water density)*g = 294 Newtons
The box's mass is M g = 980 N
Force required to lift = 686 N
(b) same approach, but the box weighs 686 N
Force required to lift = 686  294

physics  lisa, Tuesday, November 27, 2012 at 2:15pm
thank you very much!
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