If the cuboid is mounted on the top of an inverted pointed object, the pressure exerted by the set-up on the sand ________.
Answers
Cuboid and its surface area
Cuboid: It is a rectangular parallelepiped whose faces are not equal in length. A solid cuboid has six faces. A pair of opposite faces are equal and have same surface area.
In the given cuboid (figure)
NCERT Class 9 Science Lab Manual - Pressure 1
Area of face ABCD
i. e. Surface Area = length x breadth = 15 cm x 10 cm =150 cm2
Area of face BCGF
Surface Area A2= length x breadth = 10 cm * 5 cm = 50 cm2
Area of face ABFE
Surface Area A3 = length x breadth = 15 cm x 5 cm = 75 cm2
Materials Required
A solid cuboid made of iron with dimensions 5 cm x 10 cm x 15 cm, a tray with fine sand/beach sand (Tray: 10 x 20 x 30 cm), spring balance, sting and clamp stand.
A. Determination of weight of the given cuboid
Procedure
Tie the string to the cuboid.
Note the zero error of the spring balance.
Suspend the cuboid on the hook of the spring balance that is hung on the clamp stand.
Note the reading of the spring balance. If the spring balance shows the reading in newtons, record the reading shown as the weight of the cuboid.
If the spring balance shows the reading in g, then convert the reading into newtons, as follows:
Convert the ‘g’ into kg. Multiply it with (g = 9.8 m/s2)
Observations
Number of divisions on spring balance between 0 to first (W0) reading………………. (n)
Least reading of the spring balance = \frac { { W }_{ 0 } }{ n } =……….
Reading of spring balance suspended freely in air (zero error) = ‘0’
Weight of the Cuboid =………….. N.
B. Determination of the pressure exerted by different faces of cuboid
Procedure
On a plain table keep a tray as shown in the figure.
Fill in the tray with fine sand.
Place the solid cuboid on the tray with fine sand as follows:
Case (a) Face 5 cm x 10 cm should be in contact with the sand.
Case (b) Face 10 cm x 15 cm should be in contact with the sand.
Case (c) Face 5 cm x 15 cm should be in contact with the sand.
Carefully observe the depressions made by all the three cases and record the maximum and the minimum depression caused by the cuboid using a scale.
Do the calculations to find the pressure exerted by each dimension i.e. case a, b and c.
Observation and calculations
The maximum depression in the sand is seen in case (a) .
The minimum depression in the sand is seen in case (b) .
1. The weight of the cuboid = 1 kg
2. Thrust exerted by the cuboid = (Force) = m x a
e.g. = 1 x 9.8 m/s2 = 9.8 N
Thrust exerted by any surface of the cuboid remains the same = 9.8 N.
3. Surface area
Case (a) 5 cm x 10 cm = 50 cm2 = 5 x10-3 m2
Case (b) 10 cm x 15 cm = 150 cm2 = 15 x10-3 m2
Case (c) 5 cm x 15 cm = 75 cm2 = 75 x10-4 m2
NCERT Class 9 Science Lab Manual - Pressure 2