Question 7
A tank 5 m long, 3 m wide and 2 m deep is filled with a liquid of density 800 kg m−3. What force does the liquid produce on the base of the tank? (g = 10 m s−2)
The right answer is the one marked above.
240 000 N. The pressure first: P = 2 × 800 × 10 = 16 000 Pa. The area of the base is 5 × 3 = 15 m2. So force = 16 000 × 15 = 240 000 N.
16 000 N is the pressure written out as though it were a force — multiplying by the area has been forgotten. Note that length and width play no part in the pressure but are needed for the force.