A block of wood is kept on a tabletop . The mass of wooden block is 5kg and its dimensions are 40cm x 20cm x 10cm. Find the pressure exerted by the wooden block on the tabletop if it is made to lie with its sides of dimension (a) 40cm x 10cm (b) 40cm x2O cm
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Pressure = force / area
So the bigger the area, the LOWER the pressure. For maximum pressure, the block therefore needs to be standing on a face with the SMALLEST area.
In this case, that's the face that measures 3 cm * 2 cm.
Now we need to sort out the units. The SI unit of pressure is the pascal {N/m²} So we need to convert the area of the face into square metres.
Area = 3 cm * 2 cm = 0.03 m * 0.02 m = 0.0006 m²
The force acting is just the weight force of the block.
weight = mg
where m is the mass and g is the acceleration due to gravity { g = 9.81 m/s² }
weight force = 0.0216 kg * 9.81 m/s² = 0.212 N
Maximum pressure = 0.212 N / 0.0006 m² = 353 Pa {rounded}
2. Pressure (P) at the base of a column of liquid of height h and density ρ is given by
P = ρgh
Watch the units again!
ρ for water = 1000 kg/m³
h = 250 cm = 2.5 m
g = 9.81 m/s²
P = 1000 * 9.81 * 2.5
P = 24525 Pa
So the bigger the area, the LOWER the pressure. For maximum pressure, the block therefore needs to be standing on a face with the SMALLEST area.
In this case, that's the face that measures 3 cm * 2 cm.
Now we need to sort out the units. The SI unit of pressure is the pascal {N/m²} So we need to convert the area of the face into square metres.
Area = 3 cm * 2 cm = 0.03 m * 0.02 m = 0.0006 m²
The force acting is just the weight force of the block.
weight = mg
where m is the mass and g is the acceleration due to gravity { g = 9.81 m/s² }
weight force = 0.0216 kg * 9.81 m/s² = 0.212 N
Maximum pressure = 0.212 N / 0.0006 m² = 353 Pa {rounded}
2. Pressure (P) at the base of a column of liquid of height h and density ρ is given by
P = ρgh
Watch the units again!
ρ for water = 1000 kg/m³
h = 250 cm = 2.5 m
g = 9.81 m/s²
P = 1000 * 9.81 * 2.5
P = 24525 Pa
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