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A glass shaped like a uniform straight tumbler is filled with water. Its base has area 20 cm², its top has area 20 cm², its height is 20 cm, and it holds half a litre of water. Atmospheric pressure is 1.0e5 N/m², water density is 1000 kg/m³ and g = 10 m/s². (a) Find the force the water exerts on the base of the glass. (b) Using the equilibrium of the water, find the net force exerted by the walls of the glass on the water.
- (a) 204 N, (b) 1 N downward
- (a) 200 N, (b) 5 N upward
- (a) 204 N, (b) 4 N upward
- (a) 196 N, (b) 1 N upward
Correct answer: (a) 204 N, (b) 1 N downward
Solution
The base supports both the atmosphere transmitted through the water and the hydrostatic head. The walls supply whatever vertical force is needed to keep the water in equilibrium given the top and bottom pressures and the weight.
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