The small spherical planet called \"Glob\" has a mass of 7.3e+18 kg and a radius
ID: 1498046 • Letter: T
Question
The small spherical planet called "Glob" has a mass of 7.3e+18 kg and a radius of 63000 m. An astronaut on the surface of Glob throws a rock straight up. The rock reaches a maximum height of 1700 m, above the surface of the planet, before it falls back down. What was the initial speed of the rock as it left the astronaut's hand? (Glob has no atmosphere, so no energy is lost to air friction.) (G = 6.67 x 10-11Nm2/kg2) (in m/s)
A: 2.015×101 B: 2.680×101 C: 3.565×101 D: 4.741×101 E: 6.306×101 F: 8.387×101 G: 1.115×102 H: 1.484×102Explanation / Answer
given data
m=7.3*10^18 kg
r = 63000m
height = 1700 m
G = 6.67 x 10^-11Nm2/kg2
What was the initial speed of the rock as it left the astronaut's hand?
from gravitaion
Potential energy = Kinetic energy (no energy is lost to air friction)
GMm( 1/R2 - 1/R1) = 1/2 m v^2
where R2 = R1 + h = 63000+1700 = 64700 m
GM( 1/R2 - 1/R1) = 1/2 v^2
6.67 *10^-11 * 7.3*10^18 ((1/63000) - (1/64700)) = 0.5*v^2
v=20.15 m/s
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