11th Physics: Units, Dimensions, and Errors
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Questions and Answers

A car travels the first third of a journey at a speed of 30 m/s, the second third at 40 m/s, and the last third at 50 m/s. What is the average speed of the car for the entire journey?

  • 41.2 m/s
  • 38.3 m/s (correct)
  • 39.1 m/s
  • 40 m/s

A particle's velocity is described by the function $V(x) = 3x^2 + 2x$. What is the particle's acceleration at $x = 2$?

  • 40 m/s^2
  • 28 m/s^2
  • 30 m/s^2
  • 26 m/s^2 (correct)

A ball is launched vertically upwards with an initial speed of 20 m/s. Neglecting air resistance, what is the maximum height reached by the ball? (Assume $g = 9.8 m/s^2$)

  • 20.41 m (correct)
  • 40.82 m
  • 25.51 m
  • 30.61 m

A projectile is launched with an initial velocity $U$ at an angle $\theta$ with respect to the horizontal. If the maximum height reached by the projectile is equal to its range, what is the value of $\theta$?

<p>$\theta = tan^{-1}(4)$ (B)</p> Signup and view all the answers

Two cars, A and B, are moving in the same direction. Car A has a velocity of 25 m/s and Car B has a velocity of 15 m/s. What is the magnitude of the relative velocity of Car A with respect to Car B?

<p>10 m/s (B)</p> Signup and view all the answers

In dimensional analysis, which of the following functions must have dimensionless arguments?

<p>Trigonometric functions (A)</p> Signup and view all the answers

A student measures a length four times and obtains the following values: 10.2 cm, 10.1 cm, 9.9 cm, and 10.0 cm. What is the correct way to express the final measurement, including absolute error?

<p>$(10.05 \pm 0.15)$ cm (C)</p> Signup and view all the answers

If a quantity x is calculated as $x = (a^2 * b) / c$, and the percentage errors in a, b, and c are 2%, 3%, and 4% respectively, what is the percentage error in x?

<p>9% (B)</p> Signup and view all the answers

A vernier caliper has 20 divisions on its vernier scale that coincide with 19 divisions on the main scale. If each main scale division is 1 mm, what is the least count of the caliper?

<p>0.05 mm (C)</p> Signup and view all the answers

What is the angle between two vectors $\vec{a}$ and $\vec{b}$ if their magnitudes are equal and the magnitude of their resultant is also equal to the magnitude of either vector?

<p>120° (B)</p> Signup and view all the answers

Two vectors, $\vec{a} = 2\hat{i} - \hat{j} + \hat{k}$ and $\vec{b} = \hat{i} + \hat{j} - 2\hat{k}$, define two sides of a triangle. What is the area of the triangle?

<p>$\sqrt{30}/2$ (B)</p> Signup and view all the answers

A particle moves along a straight line such that the distance traveled is directly proportional to the square of the time. What can be concluded about the velocity of the particle?

<p>It is directly proportional to time. (D)</p> Signup and view all the answers

A car travels half of its journey with a speed of 40 m/s and the remaining half with a speed of 60 m/s. What is the average speed of the car for the entire journey?

<p>48 m/s (A)</p> Signup and view all the answers

Flashcards

Dimensionless Arguments

Arguments within trigonometric, logarithmic, and exponential functions must be dimensionless.

Average Value

Sum of measurements divided by the number of measurements.

Absolute Error

The absolute difference between a single measurement and the average value.

Mean Absolute Error

Average of all the absolute errors in a set of measurements.

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Relative Error

Mean Absolute Error divided by the Average value

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Resultant Vector Magnitude

The magnitude of the resultant vector when adding two vectors a and b.

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Average Velocity

Total displacement divided by total time.

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Average Speed

Total distance traveled divided by total time.

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Average Speed (Equal Lengths)

Average speed when segments have equal lengths but different speeds, calculated using the harmonic mean.

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Displacement in nth Second

The formula to determine the displacement of an object during a specific second (nth second) of its motion.

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Projectile Motion Velocity

In projectile motion, the horizontal component of velocity remains constant, while the vertical component changes due to gravity.

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Trajectory Equation

The equation describing the path of a projectile in terms of its horizontal position (x) and vertical position (y). Influenced by launch angle, gravity and initial velocity.

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Relative Displacement

The difference in displacement between two objects, found by subtracting the displacement vector of object B from that of object A.

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Study Notes

  • Lecture about formulas and concepts for the JEE and NEET physics exams for class 11
  • Conceptual understanding and derivation is more important than Rote memorization
  • The notes summarize formulas and provide context, not to solve questions

Units, Dimensions, and Errors

  • Arguments of trigonometric, logarithmic, and exponential functions must be dimensionless in dimensional analysis
  • Average value is the sum of measurements divided by the number of measurements
  • Absolute error = |measurement - average value|
  • Mean absolute error = average of all absolute errors
  • Final measurement = mean ± mean absolute error
  • Relative Error (Fractional Error) = Mean Absolute Error / Average value
  • Percentage Error = Relative Error * 100
  • For x = (a^A * b^B) / (c^C * d^D), the % error in x = A(% error in a) + B(% error in b) + C(% error in c) + D(% error in d)
  • If x = a+b, absolute error in x = absolute error in a + absolute error in b
  • If x = a-b, absolute error in x = absolute error in a + absolute error in b
  • Least count of vernier calipers = smallest division on main scale - smallest division on vernier scale
  • Total reading with calipers = main scale reading + vernier scale reading
  • Corrected value = Total Reading - Zero Error; instruments showing readings when they should be zero have positive error.

Vectors

  • |a + b| = √(a² + b² + 2ab cos θ), where θ is the angle between vectors a and b.
  • |a - b| = √(a² + b² - 2ab cos θ)
  • When |a| = |b| = x, then |a + b| = 2x cos(θ/2) and |a - b| = 2x sin(θ/2)
  • Magnitude of a vector = √(x² + y² + z²)
  • Scalar product: a â‹… b = |a||b| cos θ
  • Cross product magnitude: |a × b| = |a||b| sin θ
  • Area of triangle with sides a and b: 1/2 * |a × b|
  • Area of parallelogram with adjacent sides a and b: |a × b|
  • Cross product components involves calculating the determinant of a matrix

Kinematics Part 1

  • Average velocity: total displacement / total time
  • Average speed: total distance / total time
  • For equal time intervals, average speed is the arithmetic mean
  • If a body travels equal lengths at different speeds, the average speed formula uses the harmonic mean
  • Standard equations of motion: vf = vi + at, s = vi(t) + 0.5at², vf² = vi² + 2as
  • General Acceleration Formula: a = dV/dt
  • If V= f(x), then a = V(dV/dx)
  • Displacement in nth second = u + a/2(2n - 1)
  • For vertical launch with speed u, max height h = u² / (2g), time of flight T = 2u / g

Kinematics Part 2

  • Projectile motion has a constant x-component of velocity and a changing y-component
  • Time of flight = (2 * U * sin(theta)) / g
  • Max height = (U^2 * sin^2(theta)) / (2g)
  • Trajectory Equation: y = tan(theta) * x - (g * x^2) / (2 * U^2 * cos^2(theta))
  • For projectile motion, 4 * hMax / Range = tan(theta)
  • For projectile motion on an incline: Time of Flight = (2 * U * sin(alpha)) / (g * cos(theta)), Range = (2 * U^2 * sin(alpha) * cos(theta + alpha)) / (g * cos^2(theta))

Relative Motion

  • Relative Displacement = Sa - Sb
  • Relative Velocity = Va - Vb

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Description

A concise overview of units, dimensions, and error analysis for 11th-grade physics, tailored for JEE and NEET exam preparation. The lecture emphasizes understanding and derivation instead of rote memorization. Key concepts include dimensional analysis, error types (absolute, mean absolute, relative, percentage), and their propagation.

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