A spring stores 18 J energy when stretched 3 cm. Force constant k is:
A. 2 N/m
B. 6 N/m
C. 40000 N/m
D. 200 N/m
Answer: Option C
Solution (By JKSSB Mock Tests)
Elastic PE: U = ½kx² ⇒ k = 2U/x². x = 3 cm = 0.03 m. k = 2×18/(0.03)² = 36/0.0009 = 40000 N/m. Unit conversion critical: cm to m. Memory aid: 'k = 2U/x²; always use SI units'. Tests spring energy formula application with unit conversion, frequently appearing in competitive exams.
Explanation:
Convex mirror and concave lens always produce virtual images. Concave mirror and convex lens can produce real images under certain conditions. So convex mirror always virtual.
Explanation:
A rainbow is formed by sunlight interacting with water droplets. As light enters the droplet, it undergoes refraction and dispersion (separating into colors). The light then strikes the back of the droplet and undergoes total internal reflection. Finally, it undergoes a second refraction as it exits, spreading the spectrum out for the observer to see.
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