The force beared by a wall on which water strikes normally at a speed of 10m/sec and at a discharge of 0.0001m3/sec is__________________?
Correct answer: A. 1 N
- A. 1 N
- B. 10 N
- C. 100 N
- D. none
Explanation
The force needed to stop a normally striking water jet is F = ρQv = (1000 kg/m^3)(0.0001 m^3/s)(10 m/s) = 1 kg m/s^2 = 1 N, so option a is correct. The likely trap is option b, 10 N, which comes from using the speed without correctly calculating the mass flow rate of water.
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About Fluid Drag
Fluid drag is the resistive force exerted by a liquid or gas on an object moving through it, and its value depends on speed, fluid density, shape and exposed area. Questions examine drag at low and high speeds, terminal velocity when drag balances weight, and the difference between drag and ordinary solid friction.
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