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Gravitational Field Strength & Satellites. Gravitational Field Strength. Gravitational force per unit mass on an object g = F g / m (units = N/Kg) g = gravitational field strength F g = Force of gravity (also weight) m = mass . Gravitational Field Strength. Example Problem:
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Gravitational Field Strength • Gravitational force per unit mass on an object g = Fg / m (units = N/Kg) • g = gravitational field strength • Fg = Force of gravity (also weight) • m = mass
Gravitational Field Strength • Example Problem: While in orbit in the space shuttle, the gravitational field strength on an astronaut is 7.83 N/Kg. • How much does an 80 kg astronaut weigh on the shuttle? • How much does the astronaut weigh on Earth?
Gravitational Field Strength Problem How much does an 80 kg astronaut weigh on the shuttle? g = Fg / m (solve for Fg) Fg =(7.83 N/Kg) x (80 Kg) = 626.4 N (we don’t express in N) = 626.4 N x .22 lbs/N = 137.8 lbs
Gravitational Field Strength Problem How much does the astronaut weigh on Earth? Fg = (9.8 N/Kg) x (80 Kg) = 784 N = (784 N) x (.22 lbs/N) = 172.5 lbs
Satellite Speed & Period • Remember, to solve for altitude you must include the radius of the Earth • To solve for altitude, use the equation a = v2(solve for “r”) r speed / velocity: v = sqrt Gxm / r period: T = 2π x sqrt R3 GM
Satellite Speed & Period • When solving these problems, you use the “M” – the large mass that the satellite is revolving around • “R” – the radius / altitude of the satellite above the object it is orbiting