Answer on Question #62531, Physics / Mechanics | Relativity
How fast would rain drops hit the ground after falling from a cloud 1 kilometer above the Earth's surface
Solution:
Without air resistance, everything falls at the same acceleration, 9.81 m/s/s 9.81 \, \text{m/s/s} 9.81 m/s/s . That is, every second, it goes 9.81 meters per second faster.
The speed is
v = 2 g h v = \sqrt{2 g h} v = 2 g h
Free fall is independent of the mass of the body. It only depends on height and time period for which body is thrown.
v = 2 ⋅ ( 9.81 m/s 2 ) ⋅ ( 1000 m ) = 140 m/s v = \sqrt{2 \cdot (9.81 \, \text{m/s}^2) \cdot (1000 \, \text{m})} = 140 \, \text{m/s} v = 2 ⋅ ( 9.81 m/s 2 ) ⋅ ( 1000 m ) = 140 m/s
Free Fall Formula is
y = y 0 − 1 2 g t 2 y = y_0 - \frac{1}{2} g t^2 y = y 0 − 2 1 g t 2
where y = 0 y = 0 y = 0 , y 0 = 1000 m y_0 = 1000 \, \text{m} y 0 = 1000 m and g = − 9.81 m/s 2 g = -9.81 \, \text{m/s}^2 g = − 9.81 m/s 2 is acceleration.
Thus, time of fall of the drop is
t = 2 ( y 0 − y ) g = 2 h g = 2 ⋅ 1000 9.81 ≈ 14.3 s t = \sqrt{\frac{2 (y_0 - y)}{g}} = \sqrt{\frac{2 h}{g}} = \sqrt{\frac{2 \cdot 1000}{9.81}} \approx 14.3 \, \text{s} t = g 2 ( y 0 − y ) = g 2 h = 9.81 2 ⋅ 1000 ≈ 14.3 s
Answer: 140 m/s 140 \, \text{m/s} 140 m/s ; 14.3 s 14.3 \, \text{s} 14.3 s
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