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Physics help plz desperate... Physics !!!?
1) A coin is placed 14.5 cm from the axis of a rotating turntable of variable speed. When the speed of the turntable is slowly increased, the coin remains fixed on the turntable until a rate of 40 rpm is reached, at which point the coin slides off. What is the coefficient of static friction between the coin and the turntable?
2) Suppose that a binary star system consists of two stars of equal mass. They are observed to be separated by 340 million kilometers and take 5.0 Earth years to orbit about a point midway between them. What is the mass of each?
______ kg
3) During an Apollo lunar landing mission, the command module continued to orbit the Moon at an altitude of about 90 km. How long did it take to go around the Moon once?
____ min
2 Answers
- WoodsmanLv 79 years agoFavorite Answer
1) At threshold, friction acceleration = centripetal acceleration
µg = ω²r
µ * 9.8m/s² = (40rev/min * 2πrad/rev * 1min/60s)² * 0.145m = 2.54 m/s²
µ = 0.26
2) For orbit, centripetal acceleration = gravitational acceleration
ω²r = GM/r²
ω = 2π/T = 2π/(5yrs * 365.25days/yr * 24hr/day * 3600s/hr)² = 2.52e-16 rad/s
G = 6.674e−11 N·m²/kg²
r = ½ * 3.4e11 m = 1.7e11 m
Solve for M.
3) Again, ω²r = (2π/T)²r = GM/r²
G = above
M = mass of moon, look up
r = radius of orbit = radius of moon (look up) + 90 km
Solve for T, convert to minutes.
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