Unit notes and practice questions
Everything here is for unit 3 of the Grade 10 Physics textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.
The cards filed under this chapter on the Grade 10 Physics page. Open one at a time.
When you use it
Use when solving for unknown forces or positions on a balanced, non moving rigid body.
Watch out
A system is only in complete static equilibrium when both net force is zero and net torque is zero at the same time.
Drafted from Grade 10 Physics, pages 60-81, then checked twice before it went up
When you use it
Use to determine how many times a substance is denser than water.
Watch out
Specific gravity is a pure ratio and has no units. Ensure both densities use identical units before dividing.
Drafted from Grade 10 Physics, pages 60-81, then checked twice before it went up
When you use it
Use to calculate the turning effect of a force applied at a distance from a pivot.
Watch out
Distance must be measured from the pivot point, and only the force component perpendicular to the lever arm produces torque.
Drafted from Grade 10 Physics, pages 60-81, then checked twice before it went up
When you use it
Use to calculate the stretch, tensile stress, tensile strain, or deformation of a solid material within its elastic limit.
Watch out
When wire diameter is given, use area = pi times diameter squared divided by 4, not just diameter squared.
Drafted from Grade 10 Physics, pages 60-81, then checked twice before it went up
10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.
Question 1
What is the physical property of a solid material that allows it to return to its original shape after an applied stretching force is removed?
Answer: B Elasticity
Why
Elasticity is the property of a material by which it returns to its original shape and size when the applied force or load is removed.
Question 2
During a classroom activity, a piece of brass sinks in water while a block of wood floats. Why does this happen?
Answer: A Brass has a greater density than water, whereas wood has a lower density than water.
Why
An object sinks if its density is greater than the density of the liquid, and it floats if its density is lower. Brass is denser than water, while wood is less dense.
Question 3
Which condition represents the first condition of static equilibrium for a rigid body?
Answer: B The net force acting on the body must be zero.
Why
The first condition of equilibrium states that the vector sum of all external forces acting on the body must be zero (net force = 0), meaning ∑Fx = 0 and ∑Fy = 0.
Question 4
Tensile strain is calculated by dividing the change in length (ΔL) by the original length (L0). What is the unit of tensile strain?
Answer: C Dimensionless (it has no units)
Why
Strain is a ratio of two lengths (ΔL / L0), so the units cancel out. Therefore, strain is a dimensionless quantity.
Question 5
A student calculates the average density of the Earth to be 5.54 × 103 kg/m3. If the density of water is 1.0 × 103 kg/m3, what is the specific gravity (SG) of the Earth?
Answer: C 5.54
Why
Specific gravity is the ratio of the density of a substance to the density of water: SG = ρEarth / ρwater = (5.54 × 103 kg/m3) / (1.0 × 103 kg/m3) = 5.54.
Question 6
A wire in a physics laboratory in Hawassa has an original length of 4.0 m. When pulled, its length increases by 0.24 mm. What is the tensile strain in the wire?
Answer: A 6.0 × 10^-5
Why
Convert 0.24 mm to meters: 0.24 × 10-3 m. Then, Tensile Strain = ΔL / L0 = (0.24 × 10-3 m) / 4.0 m = 6.0 × 10-5.
Question 7
What is the maximum stress that a material can withstand while still returning to its original shape when the force is removed?
Answer: D Elastic limit
Why
The elastic limit refers to the maximum value of stress for which a material shows elastic behavior. Beyond this limit, permanent plastic deformation takes place.
Question 8
Two children balance horizontally on a seesaw. Child 1 has a mass of 26.0 kg and sits 1.60 m from the pivot. If Child 2 has a mass of 32.0 kg, at what distance from the pivot must Child 2 sit?
Answer: B 1.30 m
Why
For rotational balance, the net torque is zero: (m1)(g)(r1) = (m2)(g)(r2). Thus, r2 = (26.0 kg × 1.60 m) / 32.0 kg = 1.30 m.
Question 9
A wire with a cross-sectional area of 3.14 × 10-6 m2 supports a suspended mass of 2.0 kg. Using g = 9.8 N/kg, what is the tensile stress in the wire?
Answer: A 6.24 × 10^6 N/m^2
Why
Tensile stress = F / A = (mg) / A = (2.0 kg × 9.8 N/kg) / (3.14 × 10-6 m2) = 19.6 N / (3.14 × 10-6 m2) = 6.24 × 106 N/m2.
Question 10
A person standing at the end of a board creates a torque of 1800 N·m about a support post 4.0 m away. Taking g = 9.8 N/kg, what is the mass of the person?
Answer: C 45.9 kg
Why
Torque is given by τ = F × r = (mg) × r. Solving for mass: m = τ / (g × r) = 1800 N·m / (9.8 N/kg × 4.0 m) = 1800 / 39.2 = 45.9 kg.
The app holds 12 questions on this unit, marked as you go. These are the first 10.
Unit 3 runs from page 60 to page 81 of the Ministry of Education edition.
Ministry of Education edition, English, 212 pages
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