Class 9 Physics Chapter 6 Mechanical Properties of Matter explains how different materials behave when forces act on them. In everyday life, objects may stretch, compress, or change shape when a force is applied. These changes help us understand the strength, elasticity, and other physical properties of matter.
In this chapter, students learn about deformation of solids, which describes the change in shape or size of a solid when a force is applied. The relationship between force and the resulting change in length is explained through Hooke’s Law, an important principle used to study elasticity. The concept of density helps us understand how mass is distributed in a substance and why some objects float while others sink.
The chapter also introduces pressure, which is defined as force acting on a unit area. Students study pressure in liquids, where pressure increases with depth, and atmospheric pressure, the pressure exerted by the air surrounding the Earth. Another important concept is Pascal’s Law, which explains how pressure applied to a confined fluid is transmitted equally in all directions. This principle is widely used in hydraulic systems such as hydraulic lifts and brakes.
These topics are very important because they help explain many real-life phenomena, including water pressure in dams, operation of hydraulic machines, and the behavior of materials under different forces.
MCQs – Class 9 Physics Chapter 6 Mechanical Properties of Matter
Q1: The principle of a hydraulic press is based on:
(a) Hooke’s law
(b) Pascal’s law ✅
(c) Principle of conservation of energy
(d) Principle of conservation of momentum
Q2: Hooke’s Law is given by:
(a) F = ma
(b) F = mv²
(c) F = kx ✅
(d) F = ½mv²
Q3: Which device operates based on Hooke’s Law?
(a) Thermometer
(b) Spring balance ✅
(c) Hydrometer
(d) Barometer
Q4: What is the formula to calculate the density of a substance?
(a) Density = Volume / Mass
(b) Density = Mass × Volume
(c) Density = Mass / Volume ✅
(d) Density = Force / Area
Q5: What is the SI unit of density?
(a) g/cm³
(b) kg/m³ ✅
(c) N/m²
(d) kg/cm²
Q6: What is the definition of pressure?
(a) Force per unit mass
(b) Force per unit time
(c) Force per unit area ✅
(d) Mass per unit area
Q7: The unit used to express standard atmospheric pressure is:
(a) 1000 Pa
(b) 1 Pa
(c) 1.013 × 10⁵ Pa ✅
(d) 76 Pa
Important Short Questions – Class 9 Physics Chapter 6
Q1: State Pascal’s Law. Give an application of Pascal’s Law.
Answer:
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Pascal’s Law: When pressure is applied at one point in an enclosed fluid, it is transmitted equally in all directions without any loss.
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Application: Hydraulic press and hydraulic brakes in vehicles work on Pascal’s Law.
Q2: What is Hooke’s Law? Does an object remain elastic beyond the elastic limit? Give reason.
Answer:
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Hooke’s Law: The extension in an elastic object is directly proportional to the applied force, provided the elastic limit is not exceeded.
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Beyond Elastic Limit: No, the object does not remain elastic beyond its elastic limit because it will undergo permanent deformation and will not return to its original shape.
Q3: State the basic principle used in the hydraulic brake system of automobiles.
Answer:
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Hydraulic brakes work on Pascal’s Law, which states that pressure applied at one point of an enclosed fluid is transmitted equally in all directions.
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When the brake pedal is pressed, the fluid transfers equal pressure to the brake pads on all wheels, enabling uniform braking.
Q4: Define elasticity.
Answer:
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Elasticity is the property of a material by which it returns to its original shape and size after the deforming force is removed.
Q5: What is the spring constant?
Answer:
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The spring constant is a measure of the stiffness of a spring. A larger value means a stiffer spring.
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Unit: Newton per meter (N/m).
Q6: What is atmospheric pressure and how is it produced?
Answer:
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Atmospheric pressure is the pressure exerted by the weight of air molecules in the atmosphere.
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It is produced due to constant collisions of air molecules with objects and surfaces.
📥 Download Class 9 Physics Chapter 6 Notes – Mechanical Properties of Matter
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Clear explanations of all topics
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Solved MCQs
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Important Short Questions
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Important Long Questions