NEET UG 2021 previous year paper practice · PYQ-pattern set

NEET UG 2021 PYQ-pattern questions

Showing 10 of the 20 PYQ-pattern questions in this set — freshly worded in that year's pattern, not the original questions. Answers and solutions open under each question.

1. Q1 · Thermodynamics

   An ideal gas is heated at constant pressure from 27°C to 127°C. If the initial volume is V, what is the final volume?

   • A. 4V/3
   • B. 3V/2
   • C. 2V
   • D. 127V/27
   Answer and solution

   Answer: A

   At constant pressure, V/T = constant. V₁/T₁ = V₂/T₂. Converting to Kelvin: V/300 = V₂/400, so V₂ = 400V/300 = 4V/3.

2. Q2 · Gravitation

   The ratio of the orbital speeds of two satellites revolving around Earth in circular orbits at heights R and 3R from Earth's surface (where R is Earth's radius) is:

   • A. √2 : 1
   • B. 2 : 1
   • C. 1 : 1
   • D. 4 : 1
   Answer and solution

   Answer: A

   Orbital speed v ∝ 1/√r. For heights R and 3R, orbital radii are 2R and 4R respectively. Ratio v₁/v₂ = √(4R/2R) = √2, so v₁:v₂ = √2:1.

3. Q3 · Work, Energy and Power

   A particle of mass 0.5 kg moves in a force field where the potential energy U = 8x² - 4x + 10 joules (x in meters). What is the magnitude of force acting on it at x = 1 m?

   • A. 8 N
   • B. 12 N
   • C. 14 N
   • D. 16 N
   Answer and solution

   Answer: B

   Force F = -dU/dx = -(16x - 4). At x = 1 m, F = -(16 - 4) = -12 N. Magnitude is 12 N.

4. Q4 · Behaviour of Perfect Gases and Kinetic Theory

   The root mean square (rms) speed of oxygen molecules at a certain temperature is 460 m/s. What is the rms speed of hydrogen molecules at the same temperature? (Molecular mass: O₂ = 32, H₂ = 2)

   • A. 1840 m/s
   • B. 920 m/s
   • C. 115 m/s
   • D. 230 m/s
   Answer and solution

   Answer: A

   vrms ∝ 1/√M. Therefore, vH₂/vO₂ = √(MO₂/MH₂) = √(32/2) = 4. So vH₂ = 4 × 460 = 1840 m/s.

5. Q5 · Current Electricity

   A wire of resistance 12 Ω is cut into three equal parts. These parts are then connected in parallel. The equivalent resistance of the combination is:

   • A. 4 Ω
   • B. 12 Ω
   • C. 1.33 Ω
   • D. 36 Ω
   Answer and solution

   Answer: C

   Each part has resistance 12/3 = 4 Ω. When three 4 Ω resistors are connected in parallel: 1/R = 1/4 + 1/4 + 1/4 = 3/4, so R = 4/3 = 1.33 Ω.

6. Q6 · Motion of System of Particles and Rigid Body

   A solid sphere of mass M and radius R is rolling without slipping on a horizontal surface with linear velocity v. The ratio of its rotational kinetic energy to its total kinetic energy is:

   • A. 2:5
   • B. 2:7
   • C. 3:5
   • D. 5:7
   Answer and solution

   Answer: B

   For a solid sphere, I = (2/5)MR². Rotational KE = ½Iω² = ½(2/5)MR²(v/R)² = (1/5)Mv². Translational KE = ½Mv². Total KE = (1/5)Mv² + ½Mv² = (7/10)Mv². Ratio = (1/5)Mv² : (7/10)Mv² = 2:7.

7. Q7 · Kinematics

   A ball is dropped from a height of 45 m. The time taken to reach the ground is (g = 10 m/s²):

   • A. 2 s
   • B. 3 s
   • C. 4 s
   • D. 4.5 s
   Answer and solution

   Answer: B

   Using s = ½gt², we get 45 = ½ × 10 × t², so t² = 9, giving t = 3 s.

8. Q8 · Properties of Bulk Matter

   A metal wire of length 2 m and cross-sectional area 2 × 10⁻⁶ m² is stretched by 1 mm when a force of 200 N is applied. The Young's modulus of the material is:

   • A. 1 × 10¹¹ N/m²
   • B. 2 × 10¹¹ N/m²
   • C. 3 × 10¹¹ N/m²
   • D. 4 × 10¹¹ N/m²
   Answer and solution

   Answer: B

   Young's modulus Y = (F/A)/(ΔL/L) = (200/(2×10⁻⁶))/(1×10⁻³/2) = (10⁸)/(5×10⁻⁴) = 2 × 10¹¹ N/m².

9. Q9 · Thermodynamics

   The efficiency of a Carnot engine operating between temperatures 400 K (source) and 300 K (sink) is:

   • A. 20%
   • B. 25%
   • C. 30%
   • D. 40%
   Answer and solution

   Answer: B

   Efficiency η = 1 - (T₂/T₁) = 1 - (300/400) = 1 - 0.75 = 0.25 = 25%.

10. Q10 · Current Electricity

    A current of 3 A flows through a resistor of 12 Ω for 5 minutes. The heat produced in the resistor is:

    • A. 32.4 kJ
    • B. 54.0 kJ
    • C. 64.8 kJ
    • D. 108.0 kJ
    Answer and solution

    Answer: A

    Heat H = I²Rt = (3)² × 12 × (5×60) = 9 × 12 × 300 = 32400 J = 32.4 kJ.