Secondary 3 Physics Mechanics Quiz

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Secondary 3 Physics Quiz - Mechanics

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 60

Duration: 60 Minutes
Total Marks: 60 Marks

Instructions:

• Answer all questions.
• For calculations, show all working clearly.
• Use $g = 10\text{ m/s}^2$ unless otherwise stated.
• Write your answers in the spaces provided.

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Section A: Kinematics (Questions 1–6)

1. Define the term velocity and state its SI unit. [2]
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2. A car travels at a constant speed of $15\text{ m/s}$ for 10 seconds and then decelerates uniformly to a stop in 5 seconds. Calculate the total distance traveled. [3]
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3. Describe the difference between uniform acceleration and non-uniform acceleration. [2]
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4. A stone is dropped from the top of a building. Calculate the velocity of the stone after 3 seconds of free fall, ignoring air resistance. [2]
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5. A velocity-time graph shows a straight line with a negative gradient that does not cross the x-axis. What does the gradient of this line represent, and what is the state of motion of the object? [2]
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6. An object is thrown vertically upwards with an initial velocity of $20\text{ m/s}$. Calculate the maximum height reached by the object. [3]
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Section B: Dynamics (Questions 7–13)

7. Distinguish between mass and weight. [2]
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8. A box of mass $5\text{ kg}$ is pushed across a smooth horizontal floor with a force of $20\text{ N}$. Calculate the acceleration of the box. [2]
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9. Explain why a passenger in a car jerks forward when the car suddenly brakes. Relate your answer to the concept of inertia. [2]
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10. A $2\text{ kg}$ object is falling through the air. At a certain point, the air resistance is $15\text{ N}$. Calculate the net force acting on the object and its acceleration. [3]
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11. Describe the conditions under which an object falling through a fluid reaches terminal velocity. [3]
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12. A block of mass $3\text{ kg}$ is pulled up a rough inclined plane at a constant speed. If the component of weight acting down the slope is $12\text{ N}$, what is the magnitude of the frictional force acting on the block? [2]
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13. Two forces, $F_1 = 10\text{ N}$ East and $F_2 = 10\text{ N}$ North, act on a point mass. Calculate the magnitude and direction of the resultant force. [3]
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Section C: Turning Effects and Pressure (Questions 14–17)

14. Define the moment of a force and state its SI unit. [2]
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15. A uniform meter ruler is pivoted at the $50\text{ cm}$ mark. A mass of $100\text{ g}$ is placed at the $20\text{ cm}$ mark. Where must a mass of $200\text{ g}$ be placed to keep the ruler in equilibrium? [3]
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16. Explain why a tractor is designed with very wide tires in terms of pressure. [2]
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17. A cylinder of oil with density $800\text{ kg/m}^3$ has a height of $2\text{ m}$. Calculate the pressure exerted by the oil at the bottom of the cylinder. [3]
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Section D: Energy and Power (Questions 18–20)

18. State the principle of conservation of energy. [2]
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19. A ball of mass $0.5\text{ kg}$ is dropped from a height of $10\text{ m}$. Calculate its kinetic energy just before it hits the ground, assuming no energy is lost to air resistance. [3]
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20. An electric motor lifts a $20\text{ kg}$ load through a vertical height of $4\text{ m}$ in $5\text{ seconds}$. Calculate the useful power output of the motor. [3]
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Secondary 3 Physics Quiz - Mechanics (Answer Key)

1. Velocity Definition

• Definition: The rate of change of displacement / distance traveled in a specific direction. [1]
• Unit: $\text{m/s}$ (meters per second). [1]

2. Total Distance Calculation

• Distance 1 (constant speed): $s = v \times t = 15 \times 10 = 150\text{ m}$. [1]
• Distance 2 (deceleration): $s = \frac{1}{2}(u+v)t = \frac{1}{2}(15+0) \times 5 = 37.5\text{ m}$. [1]
• Total: $150 + 37.5 = 187.5\text{ m}$. [1]

3. Acceleration Difference

• Uniform: Acceleration is constant; velocity changes by the same amount every second. [1]
• Non-uniform: Acceleration changes over time; velocity does not change at a constant rate. [1]

4. Free Fall Velocity

• $v = u + at = 0 + (10 \times 3) = 30\text{ m/s}$. [2]

5. Graph Interpretation

• Gradient represents: Acceleration (or deceleration). [1]
• State of motion: The object is decelerating (slowing down) at a constant rate. [1]

6. Maximum Height

• At max height, $v = 0$.
• $v^2 = u^2 + 2as \implies 0 = 20^2 + 2(-10)s$. [1]
• $20s = 400 \implies s = 20\text{ m}$. [2]

7. Mass vs Weight

• Mass: Amount of matter in an object / measure of inertia (kg). [1]
• Weight: Gravitational force acting on an object (N). [1]

8. Newton's Second Law

• $F = ma \implies 20 = 5 \times a$. [1]
• $a = 4\text{ m/s}^2$. [1]

9. Inertia

• Inertia is the tendency of an object to resist changes in its state of motion. [1]
• The passenger's body continues to move forward at the car's original velocity while the car stops. [1]

10. Net Force and Acceleration

• $W = mg = 2 \times 10 = 20\text{ N}$ (downward). [1]
• $F_{\text{net}} = W - \text{Air Resistance} = 20 - 15 = 5\text{ N}$ (downward). [1]
• $a = F_{\text{net}} / m = 5 / 2 = 2.5\text{ m/s}^2$. [1]

11. Terminal Velocity

• As speed increases, air resistance increases. [1]
• Eventually, air resistance equals the weight of the object. [1]
• Net force becomes zero, acceleration becomes zero, and velocity remains constant. [1]

12. Inclined Plane Friction

• At constant speed, $F_{\text{net}} = 0$. [1]
• Applied force (or balancing force) = Friction + Weight component.
• Since it's moving at constant speed, the frictional force must equal the downward force component if no other force is applied, or the net force is zero.
• $F_{\text{friction}} = 12\text{ N}$ (acting up the slope to balance the $12\text{ N}$ downward component). [1]

13. Resultant Force

• Magnitude: $\sqrt{10^2 + 10^2} = \sqrt{200} \approx 14.1\text{ N}$. [2]
• Direction: North-East (or $45^\circ$ from East). [1]

14. Moment Definition

• Definition: The product of a force and the perpendicular distance from the pivot to the line of action of the force. [1]
• Unit: $\text{Nm}$ (Newton-meter). [1]

15. Principle of Moments

• Pivot at $50\text{ cm}$.
• Anticlockwise moment: $0.1\text{ kg} \times 10 \times (50 - 20) = 1\text{ N}times 30\text{ cm} = 30\text{ N}\cdot\text{cm}$ (or $0.3\text{ Nm}$). [1]
• Clockwise moment: $0.2\text{ kg} \times 10 \times d = 2\text{ N} \times d$. [1]
• $2d = 30 \implies d = 15\text{ cm}$ from pivot.
• Position: $50 + 15 = 65\text{ cm}$ mark. [1]

16. Pressure and Tires

• Pressure $P = F/A$. [1]
• Wide tires increase the surface area $A$, which decreases the pressure exerted on the ground for the same weight $F$, preventing the tractor from sinking into soft soil. [1]

17. Fluid Pressure

• $P = h\rho g = 2 \times 800 \times 10$. [2]
• $P = 16,000\text{ Pa}$ (or $1.6 \times 10^4\text{ Pa}$). [1]

18. Conservation of Energy

• Energy cannot be created or destroyed; it can only be converted from one form to another. [2]

19. GPE to KE

• $GPE = mgh = 0.5 \times 10 \times 10 = 50\text{ J}$. [2]
• By conservation of energy, $KE = GPE = 50\text{ J}$. [1]

20. Power Calculation

• Work done $W = mgh = 20 \times 10 \times 4 = 800\text{ J}$. [2]
• Power $P = W/t = 800 / 5 = 160\text{ W}$. [1]