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hasan_researc
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Homework Statement
In each of the following, an order of magnitude estimate is required. Estimate
i) the gravitational energy of a 100kg satellite in low Earth orbit, the velocity of the satellite, and the period of the orbit.
ii) the kinetic energy of a car traveling at 70mph and the power output of
a car engine.
Homework Equations
The Attempt at a Solution
Solution:
i) U = GMm/r2, where r = radius of (low earth) orbit radius of Earth = 6400 km and mass of Earth = 6*1024 kg.
Plugging numbers gives U = 6.3*109 J.
Such a big number looks a bit odd. Is this a realistic number? (or am I worng somewhere?)
v = sqrt(GM/r), so v = 750 km/s.
Assuming a circular orbit, v = 2*pi*r/T, so the time period T = 52s. !
I think this means my velocity is wrong, which U is wrong, but where IS the mistake?
ii) 1 mile = 1.6 km.
mass of (typical) train = 2000 kg.
So, K = 0.5mv2 = 3.1*104 J.
I don't know how to work out the power.
Any help I would greatly appreciate.