Secondary 4 Pure Physics Mechanics Quiz

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Secondary 4 Pure Physics Quiz - Mechanics

Name: ____________________ Class: __________ Date: __________ Score: ________

Duration: 60 Minutes
Total Marks: 45 Marks

Instructions:

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

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Section A: Kinematics and Dynamics (Questions 1-10)

1. Define the term velocity. [1]
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2. A car accelerates uniformly from $10\text{ m/s}$ to $25\text{ m/s}$ in $3.0\text{ s}$. Calculate its acceleration. [2]
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3. State the difference between a scalar quantity and a vector quantity. [1]
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4. An object is dropped from a height of $20\text{ m}$. Calculate the time it takes to reach the ground, ignoring air resistance. [2]
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5. Describe the motion of a body that has a constant speed but a varying velocity. Give one example. [2]
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6. A box of mass $5.0\text{ kg}$ is pushed across a horizontal floor with a force of $20\text{ N}$. If the friction force is $4.0\text{ N}$, calculate the acceleration of the box. [2]
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7. State Newton's First Law of Motion. [1]
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8. Explain why a passenger in a bus tends to fall forward when the bus suddenly brakes. [2]
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9. A skydiver reaches terminal velocity during a free fall. Explain this phenomenon in terms of forces. [3]
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10. A velocity-time graph for a ball rolling up a smooth slope is a straight line with a negative gradient. What does the gradient represent? [1]
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Section B: Turning Effects and Equilibrium (Questions 11-15)

11. State the principle of moments. [2]
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12. A uniform meter rule is pivoted at the $50\text{ cm}$ mark. A $2.0\text{ N}$ weight is placed at the $10\text{ cm}$ mark. Where should a $4.0\text{ N}$ weight be placed to balance the rule? [3]
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13. Define the centre of gravity of an object. [1]
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14. Describe two ways to increase the stability of a racing car. [2]
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15. A force of $15\text{ N}$ is applied perpendicularly to a spanner at a distance of $25\text{ cm}$ from the nut. Calculate the moment of the force. [2]
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Section C: Pressure and Fluids (Questions 16-20)

16. Define pressure and state its SI unit. [2]
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17. A block of wood has a mass of $1.2\text{ kg}$ and a base area of $0.02\text{ m}^2$. Calculate the pressure it exerts on a flat table. [2]
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18. A diver is $15\text{ m}$ below the surface of a lake. Given the density of water is $1000\text{ kg/m}^3$, calculate the pressure exerted by the water on the diver. [2]
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19. A sealed tank contains air at a pressure of $120\text{ kPa}$. The tank is filled with water to a depth of $2.0\text{ m}$. Calculate the total pressure at the bottom of the tank. [3]
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20. Explain how a hydraulic press is able to lift a heavy load using a small input force. [3]
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Answer Key - Secondary 4 Pure Physics Quiz: Mechanics

1. Velocity: The rate of change of displacement / displacement per unit time in a specific direction. [1]
2. $a = \frac{v - u}{t} = \frac{25 - 10}{3.0} = \frac{15}{3} = 5.0\text{ m/s}^2$ [2]
3. Scalar has magnitude only; Vector has both magnitude and direction. [1]
4. $s = \frac{1}{2}gt^2 \Rightarrow 20 = \frac{1}{2}(10)t^2 \Rightarrow t^2 = 4 \Rightarrow t = 2.0\text{ s}$ [2]
5. The body is changing direction while maintaining the same magnitude of velocity. Example: Uniform circular motion. [2]
6. $F_{net} = ma \Rightarrow 20 - 4 = 5a \Rightarrow 16 = 5a \Rightarrow a = 3.2\text{ m/s}^2$ [2]
7. An object will remain at rest or continue to move at a constant velocity in a straight line unless acted upon by a resultant force. [1]
8. Due to inertia, the passenger's body tends to maintain its state of motion (forward velocity) while the bus slows down. [2]
9. Initially, weight is the only force, so the diver accelerates downwards. [1] As speed increases, air resistance (drag) increases. [1] Eventually, drag equals weight, resultant force is zero, and acceleration becomes zero. [1]
10. The gradient represents the constant deceleration (or negative acceleration) of the ball. [1]
11. For a body in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot. [2]
12. Anticlockwise moment = $2.0 \times (50 - 10) = 2.0 \times 40 = 80\text{ Ncm}$. [1] Clockwise moment = $4.0 \times d = 80 \Rightarrow d = 20\text{ cm}$ from pivot. [1] Position = $50 + 20 = 70\text{ cm}$ mark. [1]
13. The point through which the entire weight of an object appears to act. [1]
14. (i) Lower the centre of gravity (e.g., lower chassis). [1] (ii) Widen the base of support (e.g., wider tyres/track). [1]
15. $\text{Moment} = F \times d = 15 \times 0.25 = 3.75\text{ Nm}$ [2]
16. Pressure is the force acting per unit area. Unit: Pascal (Pa) or $\text{N/m}^2$. [2]
17. $F = mg = 1.2 \times 10 = 12\text{ N}$. [1] $P = \frac{F}{A} = \frac{12}{0.02} = 600\text{ Pa}$ [1]
18. $P = \rho gh = 1000 \times 10 \times 15 = 150,000\text{ Pa}$ (or $150\text{ kPa}$) [2]
19. $P_{water} = 1000 \times 10 \times 2.0 = 20,000\text{ Pa} = 20\text{ kPa}$. [1] $P_{total} = 120 + 20 = 140\text{ kPa}$. [2]
20. Pressure is transmitted equally throughout the enclosed liquid (Pascal's Principle). [1] A small force on a small area creates high pressure. [1] This pressure acts on a larger area at the output, resulting in a much larger force ($F = P \times A$). [1]