A 400-kg concrete block is 1 m long, 0.6 m wide, and 0.3 m high. It can exert three different pressures on a horizontal surface, depending on which face it rests on. The highest pressure is
A. 0.7 kPa.
B. 2.2 kPa.
C. 13.1 kPa.
D. 21.8 kPa.
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Pressure is defined as the force per unit area. In this case, the force is the weight of the block, which is its mass times the acceleration due to gravity. The area is the area of the face that the block is resting on.
The weight of the block is its mass times the acceleration due to gravity, which is 9.8 m/s^2. So the weight of the block is 400 kg * 9.8 m/s^2 = 3920 N.
The three possible areas that the block could rest on are 1 m * 0.6 m = 0.6 m^2, 1 m * 0.3 m = 0.3 m^2, and 0.6 m * 0.3 m = 0.18 m^2.
The pressure is the weight divided by the area. So the three possible pressures are 3920 N / 0.6 m^2 = 6533.33 Pa, 3920 N / 0.3 m^2 = 13066.67 Pa, and 3920 N / 0.18 m^2 = 21777.78 Pa.
So the highest pressure is 21777.78 Pa, or 21.8 kPa. Therefore, the answer is D. 21.8 kPa.
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