Physics Essentials: 17 flashcards
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1. Define the SI unit of force and express it in base units.
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The SI unit of force is the newton (N). In base units, 1 N = 1 kg·m/s².
2. State Newton's second law of motion in equation form and explain each symbol.
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F = ma, where F is the net force (N), m is mass (kg), and a is acceleration (m/s²).
3. A 2 kg object accelerates at 3 m/s². What is the net force acting on it?
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F = ma = 2 kg × 3 m/s² = 6 N.
4. What is the difference between mass and weight?
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Mass is the amount of matter in an object (kg), constant everywhere. Weight is the gravitational force on an object (N), W = mg, and varies with gravity.
5. Calculate the weight of a 5 kg object on Earth (g = 9.8 m/s²).
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W = mg = 5 kg × 9.8 m/s² = 49 N.
6. State Newton's third law of motion and give a real-world example.
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For every action, there is an equal and opposite reaction. Example: a rocket pushes exhaust gases downward, and the gases push the rocket upward.
7. Define work in physics and give its SI unit.
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Work is the product of force and displacement in the direction of the force: W = F·d·cosθ. SI unit is the joule (J), where 1 J = 1 N·m.
8. A 10 N force moves an object 5 m in the direction of the force. How much work is done?
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W = F·d = 10 N × 5 m = 50 J.
9. Define kinetic energy and write its formula.
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Kinetic energy is the energy an object possesses due to its motion. KE = ½ mv², where m is mass (kg) and v is speed (m/s).
10. What is the kinetic energy of a 4 kg object moving at 3 m/s?
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KE = ½ × 4 kg × (3 m/s)² = ½ × 4 × 9 = 18 J.
11. Define potential energy and give the formula for gravitational potential energy near Earth's surface.
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Potential energy is stored energy due to position or configuration. Gravitational PE = mgh, where m is mass (kg), g is gravitational acceleration (m/s²), and h is height (m).
12. A 2 kg object is lifted to a height of 10 m. What is its gravitational potential energy? (g = 9.8 m/s²)
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PE = mgh = 2 kg × 9.8 m/s² × 10 m = 196 J.
13. State the law of conservation of mechanical energy.
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In the absence of non-conservative forces (like friction), the total mechanical energy (KE + PE) of a system remains constant.
14. A ball is dropped from a height of 20 m. What is its speed just before hitting the ground? (Ignore air resistance, g = 9.8 m/s²)
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Using conservation of energy: mgh = ½ mv² → v = √(2gh) = √(2 × 9.8 × 20) = √392 ≈ 19.8 m/s.
15. Define power and give its SI unit.
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Power is the rate at which work is done or energy is transferred: P = W/t. SI unit is the watt (W), where 1 W = 1 J/s.
16. A machine does 600 J of work in 30 seconds. What is its power output?
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P = W/t = 600 J / 30 s = 20 W.
17. State Newton's first law of motion and explain the concept of inertia.
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Newton's first law: An object at rest stays at rest, and an object in motion stays in motion with constant velocity unless acted on by a net external force. Inertia is the tendency of an object to resist changes in its motion.
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