Secondary 4 Pure Physics Mechanics Quiz

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Secondary 4 Pure Physics Quiz - Mechanics

Name: ____________________
Class: ____________________
Date: ____________________
Score: ________ / 55

Duration: 60 Minutes
Total Marks: 55 Marks

Instructions:

• Answer all questions in the spaces provided.
• Use $g = 10\text{ m/s}^2$ for all gravitational calculations.
• Show all working clearly for calculation questions.

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Section A: Kinematics (Questions 1–6)

1. Define velocity and state whether it is a scalar or vector quantity. [2] \

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2. A car accelerates uniformly from $15\text{ m/s}$ to $25\text{ m/s}$ in $4.0\text{ s}$. Calculate its acceleration. [2]
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3. Describe the motion of an object if its velocity-time graph is a horizontal line above the x-axis. [1] \

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4. A stone is dropped from a bridge. It takes $2.5\text{ s}$ to hit the water. Calculate the height of the bridge. [3]
   
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5. Explain the difference between speed and velocity using a real-world example. [2] \

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6. A ball is thrown vertically upwards. Sketch the velocity-time graph from the moment it is thrown until it returns to the thrower's hand. [3]
   
   
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Section B: Dynamics (Questions 7–13)

7. State Newton's First Law of Motion. [2] \

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8. A box of mass $5.0\text{ kg}$ is pushed across a rough horizontal floor with a force of $30\text{ N}$. If the friction force is $10\text{ N}$, calculate the acceleration of the box. [3]
   
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9. Distinguish between mass and weight. [2] \

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10. Explain, with reference to forces, why a skydiver eventually reaches a terminal velocity. [4] \

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11. A $2.0\text{ kg}$ object is moving at a constant velocity of $10\text{ m/s}$. What is the resultant force acting on the object? Explain your answer. [2] \

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12. Draw a free-body diagram for a book resting on a table. Label all forces acting on the book. [3]
    
    
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13. A rocket is launched vertically. At a certain point, the thrust is $15,000\text{ N}$ and the weight of the rocket is $8,000\text{ N}$. Calculate the acceleration of the rocket. [3]
    
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Section C: Turning Effect of Forces & Pressure (Questions 14–20)

14. State the Principle of Moments. [2] \

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15. 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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16. Explain why a person wearing high-heeled shoes exerts more pressure on the floor than a person wearing flat shoes of the same mass. [2] \

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17. A cylindrical container with a base area of $0.02\text{ m}^2$ contains water to a height of $0.5\text{ m}$. Calculate the pressure exerted by the water at the bottom of the container. [3]
    
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18. In a hydraulic jack, the area of the small piston is $0.001\text{ m}^2$ and the large piston is $0.05\text{ m}^2$. If a force of $100\text{ N}$ is applied to the small piston, calculate the force exerted by the large piston. [3]
    
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19. Describe how the position of the centre of gravity affects the stability of an object. [3] \

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20. A manometer is used to measure the pressure difference between two gases. If the height difference of the mercury column is $15\text{ cm}$ and the density of mercury is $13,600\text{ kg/m}^3$, calculate the pressure difference. [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. Quantity: Vector. (2 marks)

2. $a = \frac{v - u}{t} = \frac{25 - 15}{4.0} = \frac{10}{4} = 2.5\text{ m/s}^2$. (2 marks)

3. The object is moving with a constant (uniform) velocity. (1 mark)

4. $s = ut + \frac{1}{2}at^2$ $s = (0)(2.5) + \frac{1}{2}(10)(2.5)^2$ $s = 5 \times 6.25 = 31.25\text{ m}$. (3 marks)

5. Speed is a scalar (magnitude only), e.g., a car moving at $60\text{ km/h}$. Velocity is a vector (magnitude and direction), e.g., a car moving at $60\text{ km/h}$ North. (2 marks)

6. Graph should show:

   • Y-axis: Velocity, X-axis: Time.
   • A straight line with a negative gradient starting from a positive value, crossing the x-axis (v=0), and ending at a negative value. (3 marks)

7. An object will remain at rest or continue to move with constant velocity unless acted upon by a resultant external force. (2 marks)

8. $F_{net} = ma \rightarrow (30 - 10) = 5.0 \times a$ $20 = 5a \rightarrow a = 4.0\text{ m/s}^2$. (3 marks)

9. Mass is the amount of matter in an object (constant everywhere, kg). Weight is the gravitational force acting on an object (varies with $g$, N). (2 marks)

10. Initially, only weight acts downwards, causing acceleration $g$. [1] As speed increases, air resistance increases. [1] The resultant force ($W - R$) decreases, so acceleration decreases. [1] When air resistance equals weight, the resultant force is zero, and the skydiver moves at a constant terminal velocity. [1] (4 marks)

11. Resultant force = $0\text{ N}$. According to Newton's First Law, if an object moves at constant velocity, the forces acting on it are balanced. (2 marks)

12. Diagram should show:

    • Weight ($W$) acting downwards from the center.
    • Normal Contact Force ($R$ or $N$) acting upwards from the table. (3 marks)

13. $F_{net} = ma \rightarrow (15,000 - 8,000) = m \times a$ Wait, mass is not given? Let's assume the weight $8,000\text{ N}$ is used to find mass: $m = 800\text{ kg}$. $7,000 = 800 \times a \rightarrow a = 8.75\text{ m/s}^2$. (3 marks)

14. For a body in rotational equilibrium, the sum of clockwise moments about any point is equal to the sum of anticlockwise moments about the same point. (2 marks)

15. Pivot at $50\text{ cm}$. Weight 1 is at $10\text{ cm}$ (distance $= 40\text{ cm}$). $2.0\text{ N} \times 40\text{ cm} = 4.0\text{ N} \times d$ $80 = 4d \rightarrow d = 20\text{ cm}$ from pivot. Position $= 50 + 20 = 70\text{ cm}$ mark. (3 marks)

16. Pressure = Force / Area. High heels have a very small contact area compared to flat shoes. For the same force (weight), a smaller area results in a larger pressure. (2 marks)

17. $P = \rho gh = 1000 \times 10 \times 0.5 = 5,000\text{ Pa}$. (3 marks)

18. $P = F_1/A_1 = 100 / 0.001 = 100,000\text{ Pa}$. $F_2 = P \times A_2 = 100,000 \times 0.05 = 5,000\text{ N}$. (3 marks)

19. A lower centre of gravity increases stability. [1] A wider base also increases stability. [1] This is because the object can be tilted further before the line of action of the weight falls outside the base. [1] (3 marks)

20. $P = \rho gh = 13,600 \times 10 \times 0.15 = 20,400\text{ Pa}$. (3 marks)