If the earth suddenly shrinks to half its present radius without any change in its mass, the duration of a day on earth will become: MCQ with Answer and Explanation
If the earth suddenly shrinks to half its present radius without any change in its mass, the duration of a day on earth will become:
A. 12 hours
B. 6 hours
C. 48 hours
D. 24 hours
Answer: Option B
Solution (By JKSSB Mock Tests)
By conservation of angular momentum: I1w1 = I2w2. Moment of inertia of a solid sphere is 2/5 MR^2. So, (R1^2) * (2pi/T1) = (R2^2) * (2pi/T2). If radius halves, R2 = R1/2. R1^2 / T1 = (R1/2)^2 / T2. T2 = T1 / 4. A day is 24 hours, so 24/4 = exactly 6 hours.
Explanation:
Work W = F·d = Fd cosθ. cos0° = 1 gives maximum work. At 90°, cos90° = 0, work zero. For given magnitudes, maximum when force parallel to displacement. This is basic definition.
Explanation:
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.
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