A ball thrown upward returns to thrower after 6 s. Maximum height reached (g=10 m/s²) is
A. 45 m
B. 180 m
C. 30 m
D. 90 m
Answer: Option A
Solution (By JKSSB Mock Tests)
Total time of flight T = 2u/g => u = gT/2 = 10×6/2 = 30 m/s. Max height H = u²/(2g) = 900/20 = 45 m. Alternatively, time to max height = 3 s, H = ½g t² = ½×10×9 = 45 m.
Explanation:
First law of thermodynamics: Energy is conserved in an isolated system. It changes forms (kinetic to potential etc.) but total constant. Perpetual motion machine impossible.
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