EasyPhysics
+4 / -1
Which of the following is not the unit of length :
A
micron
B
light year
C
angstrom
D
radian
Explanation
Micron, light year aur angstrom length ki units hain. Radian plane angle ki SI unit hai. 92. If B is magnetic field and μ₀ is permeability of free space, then the dimensions of (B/μ₀) is A) ML² T⁻² A⁻¹ B) L⁻¹ A C) MT⁻² A⁻¹ D) LT⁻² A⁻¹ ANSWER: B MARKS: 4 NEGATIVE: 1 DIFFICULTY: easy EXPLANATION: Ampere's circuital law se, ∮B·dl = μ₀I hota hai. Isliye B/μ₀ = I/L. Dimensions ke hisaab se [B/μ₀] = [A] / [L] = [L⁻¹ A]. 93. A stone is dropped from a building, and 2 seconds later another stone is dropped. (Both are dropped from rest.) How far apart are the two stones by the time the first one has reached a speed of 30 m/s ? A) 80 m B) 100 m C) 60 m D) 40 m ANSWER: D MARKS: 4 NEGATIVE: 1 DIFFICULTY: easy EXPLANATION: Pehle stone ke liye, v = gt ⇒ 30 = 10t, isliye t = 3 s. Distance s₁ = ½gt² = 45 m. Doosra stone 2 s baad phenka gaya, toh wo sirf 1 s ke liye gira. Distance s₂ = 5 m. Separation = 40 m. 94. A man can swim at a speed of 3 km/h in still water. He wants to cross a 500 m wide river flowing at 2 km/h. He keep himself always at an angle to 120° with the river flow while swimming. The time taken to cross the river is : A) 3/2 h B) 1/6 h C) 1/(3√3) h D) none ANSWER: C MARKS: 4 NEGATIVE: 1 DIFFICULTY: easy EXPLANATION: River flow se angle 120° hai, toh bank ke normal se angle 30° hoga. Velocity ka perpendicular component = 3 cos 30° = 3√3/2 km/h. Distance = 0.5 km. Time = 1/(3√3) h. 95. A wire has a mass (0.3 ± 0.003) g, radius (0.5 ± 0.005) mm and length (6 ± 0.06) cm. The maximum percentage error in the measurement of its density is A) 1 B) 2 C) 3 D) 4 ANSWER: D MARKS: 4 NEGATIVE: 1 DIFFICULTY: easy EXPLANATION: Density ρ = m / (πr²l). Max percentage error = (Δm/m + 2Δr/r + Δl/l) × 100 = 4%.
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