WBJEE Subjective Phy & Chem Sample Paper | WBJEE Sample Papers, Section Wise & Full Mock Tests 2025 PDF Download

Question: 1. The displacement x of a particle at time t moving under a constant force is in meters, t in seconds. Find the work done by the force in the interval from t = 0 to t = 6 second.
Ans: 
v at t = 0, – 6 m/s
v at t = 6 sec., 6 m/s
change in KE is zero ⇒ work done = 0

Question: 2. Calculate the distance above and below the surface of the earth at which the acceleration due to gravity is the same
Ans: 
on solving we get
– Rh + R² – h² = 0


Question: 3. A ray of light travelling inside a rectangular glass block of refractive index √2 is incident on the glass-air surface at an angle of incidence of 45°. Show that the ray will emerge into the air at an angle of refraction equal to 90°
Ans:  Given C = 45°

So the ray will graze the interface after refraction at an angle of 90°

Question: 4. Two cells each of same e.m.f ‘e’ but of internal resistances r¹ and r² are connected in series through an external resistance R. If the potential difference between the ends of the first cell is zero, what will be the value of R in terms r¹ and r² ?
Ans: 


Question: 5. At time t = 0, a radioactive sample has a mass of 10 gm. Calculate the expected mass of radioactive sample after two successive mean lives.
Ans:  
Two successive mean lives =
No. of nuclei after two mean lives = 
Therefore mass = 

Question: 6. Calculate the number of H+ ion present in 1 ml of a solution whose pH is 10.
Ans: pH = 10
[H⁺] = 10^–10 M
In 1000 ml solution there are 6.023 × 10¹³ H⁺ ions
In 1 ml solution there are 6.023 × 10¹⁰ H⁺ ions 

Question: 7. Give the structure of pyro-sulfuric acid. How would you prepare it? What would you observe when colourless HI is added to pyro-sulfuric acid?
Ans:  



Question: 8. Write with a balanced chemical equation how gypsum is used for the conversion of ammonia into ammonium sulfate without using H₂ SO₄ .
Ans:  Balanced reaction is
2NH₃ + CaSO₄ + CO₂ + H₂O = (NH₄ )₂ SO₄ + CaCO₃

Question: 9.  Convert phenol to p-hydroxy acetophenone in not more than 2 steps.
Ans: 

Question: 10. An organic compound ‘A’ on treatment with ammoniacal silver nitrate gives metallic silver and produces a yellow crystalline precipitate of molecular formula C₉H₁₀N₄O₄ , on treatment with Brady’s reagent. Give the structure of the organic compound ‘A’.
Ans:  Compound (A) is an aldehyde. It should be propanal CH₃CH₂CHO
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