An iron needle sinks in water, whereas an iron ship floats. This is because: MCQ with Answer and Explanation

An iron needle sinks in water, whereas an iron ship floats. This is because:
A. The ship is hollow.
B. The weight of the water displaced by the ship is greater than the weight of the ship.
C. The average density of the ship is less than that of water.
D. The density of the ship is greater than that of the needle.
Answer: Option C
Solution (By JKExamLibrary)
Though the ship is made of iron, it is hollow inside and traps a large volume of air. This makes the overall or average density of the ship less than the density of water. According to the law of floatation, an object floats if its average density is less than that of the fluid. A solid iron needle has a higher density than water, so it sinks.

This question belongs to: Science Physics

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Question #1 Report Error
The process of transfer of heat in fluids by actual movement of particles is called
A. Conduction
B. Evaporation
C. Radiation
D. Convection

Correct Answer: Option D


Explanation:
Convection requires medium, movement of hot and cold masses. Land/sea breeze, trade winds, heating water. Conduction vibration transfer without particle movement.

This question belongs to: Science Physics
Question #2 Report Error
A body falls freely from rest. The ratio of distances covered in 1st, 2nd, and 3rd seconds is
A. 1:4:9
B. 1:2:3
C. 1:3:5
D. 1:1:1

Correct Answer: Option C


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s_nth = u + (g/2)(2n-1). u=0 => s ∝ (2n-1). So 1, 3, 5. Classic kinematic ratio.

This question belongs to: Science Physics
Question #3 Report Error
The speed of sound in air at 0°C is approximately 332 m/s. At 27°C, it will be approximately:
A. 360 m/s
B. 332 m/s
C. 340 m/s
D. 350 m/s

Correct Answer: Option D


Explanation:
Speed of sound in air v ∝ √T, where T is absolute temperature in Kelvin. T₀ = 0°C = 273 K, v₀ = 332 m/s. T = 27°C = 300 K. Thus v = v₀√(T/T₀) = 332 × √(300/273) ≈ 332 × √1.099 ≈ 332 × 1.048 ≈ 348 m/s ≈ 350 m/s. Approximate rule: speed increases by 0.6 m/s per °C rise, so 27×0.6≈16.2, 332+16.2≈348.2 m/s. Memory aid: 'v ∝ √T in Kelvin'. Such temperature-dependence problems test application of sound wave properties, common in competitive exams with emphasis on absolute temperature usage.

This question belongs to: Science Physics