SET 03

SET 3: Competence-Based & Conceptual Physics Questions and Answers

61. Why is it easier to carry a heavy load using a wheelbarrow than by hand?
    Answer: A wheelbarrow acts as a second-class lever which increases mechanical advantage. The fulcrum (wheel) is at one end, the load is in the middle, and the effort is at the other end. This reduces the force needed to lift the load.
    Example: In construction sites, workers move cement using wheelbarrows instead of lifting bags.
62. State the energy changes that take place in a hydroelectric power station.
    Answer: Potential energy (water at height) → Kinetic energy (falling water) → Mechanical energy (turbine rotation) → Electrical energy (generator).
    Example: Kidatu Hydro Station in Tanzania converts water energy to electricity.
63. What is the difference between mass and weight?
    Answer: Mass is the amount of matter in an object (kg), constant everywhere. Weight is the force of gravity acting on that mass (N), varies with gravitational field.
    Example: A person has 60 kg mass both on Earth and Moon, but weighs less on the Moon due to weaker gravity.
64. Explain why electric kettles are made with stainless steel or copper coils.
    Answer: These metals have high thermal conductivity and resist oxidation at high temperatures, making them efficient and durable for heating.
    Example: Boiling water using an electric kettle is quick due to copper coil’s high conductivity.
65. What physical property of waves explains the change in direction when light passes from air to glass?
    Answer: Refraction. It occurs due to a change in wave speed when crossing media with different densities.
    Example: A pencil in water appears bent due to light refraction.
66. Why does a balloon expand when taken to higher altitudes?
    Answer: Atmospheric pressure decreases with altitude, so the pressure inside the balloon becomes greater, causing it to expand.
    Example: Weather balloons swell as they rise in the atmosphere.
67. State one advantage and one disadvantage of using nuclear energy.
    Answer:
    • Advantage: Produces large amounts of energy from small fuel mass.
    • Disadvantage: Produces radioactive waste which is dangerous and hard to dispose of.
68. Explain the role of a transformer in the transmission of electricity.
    Answer: Transformers increase (step-up) voltage for transmission to reduce power loss and then decrease (step-down) voltage for safe domestic or industrial use.
    Example: Tanesco uses transformers in power grids to minimize transmission losses.
69. Why is water a better coolant than air in car engines?
    Answer: Water has a higher specific heat capacity, absorbing more heat before increasing in temperature.
    Example: Radiator systems in cars use water or coolant to regulate engine temperature.
70. Describe the energy changes when a child slides down a slide.
    Answer: Potential energy at the top is converted to kinetic energy as the child slides down.
    Example: A slide in a playground shows gravitational energy being used.
71. State the principle of flotation.
    Answer: A body floats in a fluid if the upthrust (buoyant force) is equal to the weight of the body.
    Example: Ships float because their shape displaces enough water to create a large upthrust.
72. Why are beams in bridges often designed in I-shapes?
    Answer: I-beams provide high strength with less material. They resist bending and torsion efficiently.
    Example: Railway bridges often use I-beams for structural strength and weight efficiency.
73. State the purpose of using a fuse in electrical appliances.
    Answer: A fuse protects an appliance by breaking the circuit if current exceeds a safe level.
    Example: A short circuit in an iron causes the fuse to blow, preventing fire.
74. Explain why it's cooler near the sea during the day than inland.
    Answer: Sea breeze. The land heats faster, and warm air rises allowing cooler sea air to blow in.
    Example: Coastal towns like Bagamoyo are cooler during the day.
75. Why is a convex mirror preferred for vehicle side mirrors?
    Answer: Convex mirrors provide a wider field of view and form upright, diminished images.
    Example: Car side mirrors help drivers view more traffic behind them.
76. State one condition necessary for a total solar eclipse to occur.
    Answer: The Moon must be directly between the Sun and Earth, and the Moon’s apparent diameter must completely cover the Sun.
    Example: A total eclipse observed in Tunduru in 2001.
77. Why are iron and steel magnetic but copper and aluminum are not?
    Answer: Iron and steel have unpaired electrons that align in a magnetic field, while copper and aluminum do not.
    Example: A magnet attracts nails but not copper wires.
78. What is the difference between heat and temperature?
    Answer: Heat is energy transferred due to temperature difference (measured in joules), while temperature is the degree of hotness or coldness (measured in °C or K).
    Example: A cup of tea and a bucket of warm water may have same temperature, but the bucket has more heat.
79. State two applications of electromagnetic induction.
    Answer:
    • Electric generators
    • Transformers
    Example: Bicycle dynamos use electromagnetic induction to power lights.
80. Why does a metal spoon feel colder than a wooden spoon at the same room temperature?
    Answer: Metal conducts heat away from your hand faster than wood, giving a cold sensation.
    Example: Touching iron in a cold room feels much colder than touching a book.