The Solution for GRE Physics Practice Test [21-40]
추천글 : 【GRE】 Solution for GRE Physics Practice Test
21. The period of a physical pendulum is 2π√(I / mgd), where I is the moment of inertia about the pivot point and d is the distance from the pivot to the center of mass. A circular hoop hangs from a nail on a barn wall. The mass of the hoop is 3 kilo-grams and its radius is 20 centimeters. If it is displaced slightly by a passing breeze, what is the period of the resulting oscillations?
⑴ answer: C
⑵ 계산 과정 : 질량 m과는 무관함
22. The curvature of Mars is such that its surface drops a vertical distance of 2.0 meters for every 3600 meters tangent to the surface. In addition, the gravitational acceleration near its surface is 0.4 times that near the surface of Earth. What is the speed a golf ball would need to orbit Mars near the surface, ignoring the effects of air resistance?
⑴ answer: C
⑵ 계산 과정
23. Suppose that the gravitational force law between two massive objects were F12 = r12 Gm1m2 / r122+ϵ where ϵ is a small positive number. Which of the following statements would be FALSE?
⑴ answer: D
⑵ 케플러 법칙
🄐 보존력이 정의되면 역학적 에너지 보존법칙이 정의됨
🄑 각운동량 보존법칙은 c := r(t) × r'(t)라 두면, c'(t) = r'(t) × r'(t) + r(t) × r"(t) = r(t) × r"(t) = 0
🄒, 🄔 약식 계산 : 구심력이 중력인 정적 원형 궤도 상황을 가정하면,
🄓 타원 궤도의 법칙은 중력이 거리의 제곱에 반비례하는 중심력이라는 사실과 연결됨
24. Two identical conducting spheres, A and B, carry equal charge. They are initially separated by a distance much larger than their diameters, and the force between them is F. A third identical conducting sphere, C, is uncharged. Sphere C is first touched to A, then to B, and then removed. As a result, the force between A and B is equal to
⑴ answer: D
⑵ (QA, QB) = (Q, Q) → (Q/2, Q) → (Q/2, 3Q/4)
⑶ F = kQ2
⑷ F' = k(Q/2)(3Q/4) = 3F / 8
25. Two real capacitors of equal capacitance (C1 = C2) are shown in the figure below. Initially, while the switch S is open, one of the capacitors is uncharged and the other carries charge Q0. The energy stored in the charged capacitor is U0. Sometime after the switch is closed, the capacitors C1 and C2 carry charges Q1 and Q2, respectively; the voltages across the capacitors are V1 and V2; and the energies stored in the capacitors are U1 and U2. Which of the following statements is INCORRECT?
⑴ answer: E
⑵ 커패시터
⑶ Q = CV이고 V가 공통이므로 Q0 = Q1 = Q2 → Q0 = (Q1 + Q2) / 2
⑷ U = (1/2)V2이고 V가 공통이므로 U0 = U1 = U2 → 2U0 = U1 + U2
26. A series RLC circuit is used in a radio to tune to an FM station broadcasting at 103.7 MHz. The resistance in the circuit is 10 ohms and the inductance is 2.0 microhenries. What is the best estimate of the capacitance that should be used?
⑴ answer: C
⑵ RLC 회로 : ω2 = 1 / LC → 1 / ((2 × π × 103.7 × 106)2 × 2 × 10-6) = 1.18 pF
27. In laboratory experiments, graphs are employed to determine how one measured variable depends on another. These graphs generally fall into three categories: linear, semilog (logarithmic versus linear), and log-log. Which type of graph listed in the third column below would NOT be the best for plotting data to test the relationship given in the first and second columns?
⑴ answer: D
⑵ linear : Y = aX + b의 형태
⑶ semilog : log Y = aX + b의 형태
⑷ log-log : log Y = a log X + b의 형태
🄓 linear라기보다는 반비례(inversely linear)
28. The figure below represents the trace on the screen of a cathode ray oscilloscope. The screen is graduated in centimeters. The spot on the screen moves horizontally with a constant speed of 0.5 centimeter/millisecond, and the vertical scale is 2 volts/centimeter. The signal is a superposition of two oscillations. Which of the following are most nearly the observed amplitude and frequency of these two oscillations?
⑴ answer: D
⑵ 파동의 개념
⑶ 큰 파동 : f1 = v1 / λ1 = 0.5 cm/ms / 6 cm = 1000/12 = 83 Hz. 진폭은 y축으로 1.25 cm와 대응되는 2.5 V
⑷ 작은 파동 : f2 = v2 / λ2 = 0.5 cm/ms / 1 cm = 1000/2 = 500 Hz. 진폭은 큰 파동의 절반인 1.25 V
29. The characteristic distance at which quantum gravitational effects are significant, the Planck length, can be determined from a suitable combination of the physical constants G, ℏ, and c. Which of the following correctly givens the Planck length?
⑴ answer: E
⑵ 차원해석
⑶ [ML/T2] = [G][M2 / L2] ⇔ [G] = [L3 / MT2]
⑷ [ℏ] = [E][T] = [ML2/T]
⑸ [c] = [L/T]
⑹ [G]x[ℏ]y[c]z = [L] ⇔ 3x + 2y + z = 1, -x + y = 0, -2x - y - z = 0 ⇔ x = y = 1/2, z = -3/2
30. An open-ended U-tube of uniform cross-sectional area contains water (density 1.0 gram/centimeter3) standing initially 20 centimeters from the bottom in each arm. An immiscible liquid of density 4.0 grams/centimeter3 is added to one arm until a layer 5 centimeters high forms, as shown in the figure below. What is the ratio h2/h1 of the heights of the liquid in the two arms?
⑴ answer: C
⑵ 유체의 성질
⑶ h1 - 5 + h2 = 40
⑷ 1 × (h2 - h1) = (4 - 1) × 5
⑸ ∴ h1 = 15, h2 = 30, h2/h1 = 2
31. A sphere of mass m is released from rest in a stationary viscous medium. In addition to the gravitational force of magnitude mg, the sphere experiences a retarding force of magnitude bv, where v is the speed of the sphere and b is a constant. Assume that the buoyant force is negligible. Which of the following statements about the sphere is correct?
⑴ answer: E
⑵ 점점 속도가 증가하는 것(monotonicity)은 직관에 부합함
⑶ 종단속도 mg = bvterminal ⇔ vterminal = mg / b
⑷ 실제 중력실험
32. Three equal masses m are rigidly connected to each other by massless rods of length ℓ forming an equilateral triangle, as shown below. The assembly is to be given an angular velocity ω about an axis perpendicular to the triangle. For fixed ω, the ratio of the kinetic energy of the assembly for an axis through B compared with that for an axis through A is equal to
⑴ answer: B
⑵ 강체역학
⑶ KA = 3 × (1/2) m(√3 / 3)2ℓ2 ω2
⑷ KB = 2 × (1/2) mℓ2 ω2
⑸ KB / KA = 2
33. A diatomic molecule is initially in the state 𝚿(𝚯, 𝚽) = (5Y11 + 3Y51 + 2Y5-1)/(38)1/2, where Yℓm is a spherical harmonic. If measurements are made of the total angular momentum quantum number ℓ and of the azimuthal angular momentum quantum number m, what is the probability of obtaining the result ℓ = 5?
⑴ answer: C
⑵ 오비탈 이론
⑶ 우선 38이라는 숫자는 52 + 32 + 22 임을 주목 → 오비탈은 제곱이 확률을 의미함
⑷ Y51, Y5-1이 ℓ = 5와 대응되므로 계산해야 하는 확률은 (32 + 22) / 38 = 13/38
34. When the beta-decay of 60Co nuclei is observed at low temperatures in a magnetic field that aligns the spins of the nuclei, it is found that the electrons are emitted preferentially in a direction opposite to the 60Co spin direction. Which of the following invariances is violated by this decay?
⑴ answer: D
⑵ 뇌터의 정리 : 물리계(라그랑지안/작용)가 어떤 연속 대칭을 가지면, 그에 대응하는 보존량이 생김
35. The wave function for identical fermions is anti-symmetric under particle interchange. Which of the following is a consequence of this property?
⑴ answer: A
⑵ 파울리 배타원리
36. A lump of clay whose rest mass is 4 kilograms is traveling at three-fifths the speed of light when it collides head-on with an identical lump going the opposite direction at the same speed. If the two lumps stick together and no energy is radiated away, what is the mass of the composite lump?
⑴ answer: D
⑶ E = 2 × γmc2 = m'c2 ⇔ m' = 2γm = 2 × (1 - (3/5)2)-1/2 × 4 = 10
37. An atom moving at speed 0.3c emits an electron along the same direction with speed 0.6c in the internal rest frame of the atom. The speed of the electron in the lab frame is equal to
⑴ answer: D
⑵ 상대론적 속도 덧셈 : (0.3c + 0.6c) / (1 + 0.3c × 0.6c / c2) = 0.9c / (1 + 0.18) = 0.763c
38. What is the speed of a particle having a momentum of 5 MeV/c and a total relativistic energy of 10 MeV?
⑴ answer: D
⑵ γmv = 5 / c, γmc2 = 10 → β = v/c = 0.5
39. Which of the following atoms has the lowest ionization potential?
⑴ answer: E
⑵ 이온화에너지
40. If a singly ionized helium atom in an n = 4 state emits a photon of wavelength 470 nanometers, which of the following gives the approximate final energy level, Ef, of the atom, and the n value, nf, of this final state?
⑴ answer: A
⑵ 470 nm → 자외선 → 라이만 계열(Lyman series)
입력: 2026.05.05 23:26
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