The time taken for a ball dropped from height h to reach ground is t. If dropped from height 4h, the time taken is:
A. 4t
B. t
C. t/2
D. 2t
Answer: Option D
Solution (By JKSSB Mock Tests)
Free fall: h = ½gt² ⇒ t = √(2h/g). Thus t ∝ √h. If h' = 4h, t' = √(4h/g) = 2√(h/g) = 2t. Time doubles when height quadruples. Memory aid: 'Free fall time: t ∝ √h; quadruple height ⇒ double time'. This kinematics proportional reasoning problem is frequently tested in competitive exams. Always derive the proportionality from fundamental equations; avoid assuming linear relationships for non-linear motion.
In standard AC household supply in India, the frequency of the alternating current is 50 Hz. How many times per second does the current change its direction?
Explanation:
A frequency of 50 Hz means there are 50 complete wave cycles per second. A single complete sinusoidal cycle consists of one positive half-cycle and one negative half-cycle. Therefore, the current reaches zero and reverses its direction exactly twice during each complete cycle. For 50 cycles, the current changes direction 50 * 2 = 100 times per second.
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