### JEE, NEET, Foundation & CBSE

A solid wooden block with a uniform cross section is floating in water (density ρw) with a height h₁ below water. Now a flat slab of stone is placed over the wooden block but the block still flats with a height h₂ below water. Afterwards the stone is removed from the top and pasted at the bottom of the wooden block. The wooden block now floats with a height h₃ under water. Therefore, the density of the stone is
1. [ (h₃ /(h₂ - h₁) ] ρw
2. [(h₂-h₁ )/(h₃ - h₁) ] ρw
3. [(h₂-h₃ )/(h₂ - h₁) ] ρw
4. [(h₂- h₁ )/(h₂ - h₃) ] ρw
Two particles A and B are situated 10 m apart along X axis, B being farther of A, at t = 0. Particle A is moving at 0.75 m/s parallel to +Y axis while B at 1 m/s along –X axis. After a time t they come closes to each other. Therefore, t is
1. 3.2 s
2. 4.8 s
3. 6.0 s
4. 6.4 s
When a certain metal was irradiated with light of frequency 3.2 × 10¹⁶ Hz, the photoelectrons emitted had twice the kinetic energy as did the photoelectrons emitted when the same metal was irradiated with light frequency 2.0 × 10¹⁶ Hz. The v₀ of the metal is
1. 2.4 × 10¹⁶ Hz
2. 8 × 10¹⁶ Hz
3. 8 × 10¹⁵ Hz
4. 7.2 × 10¹⁶ Hz
Standard molar enthalpy of formation of CO₂(g) is equal to (A) zero
1. Zero
2. The standard molar enthalpy of combustion of C(g)
3. The standard molar enthalpy of combustion of CO(g)
4. The standard molar enthalpy of combustion of carbon(graphite)
Which reaction is spontaneous at all temperatures at standard pressure and concentration?
1. Exothermic reaction with a decrease in entropy
2. Exothermic reaction with an increase in entropy
3. Endothermic reaction with a decrease in entropy
4. Endothermic reaction with an increase in entropy
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