4 Question Details SerCP8 7.P.042. My Notes Ask Your Teacher Use Kepler\'s third

Question

4 Question Details SerCP8 7.P.042. My Notes Ask Your Teacher Use Kepler's third law to determine how many days it takes a spacecraft to travel in an elliptical orbit from its nearest point, 6720 km from Earth's center, to its farthest point, the Moon, 4.04 x 105 km from Earth's center. Note: The average radius or "semimajor axis" is the average of the distance from Earth's center to the nearest and farthest points on the elliptical orbit. Need Help?ReadTak to a Tuter Show My Work (optional) 5. Question Details SerCP8 8.P.001 My Notes Ask Your Teacher A grinding wheel of radius 0.420 m rotating on a frictionless axle is brought to rest by applying a constant friction force tangential to its rim. The constant torque produced by this force is 71.8 N m. Find the magnitude of the friction force. Need Help? ReadTlik to Tuter

Explanation / Answer

4)The time period using Kepler's law is given by:

T = 2 pi sqrt (R^3/GM)

D = 4.04 x 10^5 km + 6720 km = 4.11 x 10^5 km

R = 4.11 x 10^8 m/2 = 2.06 x 10^8 m

T' = 2 pi sqrt [(2.06 x 10^8)^3/(6.67 x 10^-11 x 5.98 x 10^24)] = 9.297 x 10^5 s

T' = 9.297 x 10^5 s = 10.76 days

T = T'/2 = 10.76/2 = 5.38 days

Hence, T = 5.38 days

5)we know that

Torque = F r

F = T/r = 71.8/0.42 = 170.95 N

Hence, F = 171 N

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