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A small moon orbits its planet in a circular orbit at a speed of 7.5km/s. It takes 28hours to complete one full orbit. What is the mass of the planet?

Short Answer

Expert verified

The mass of the planet is1026kg.

Step by step solution

01

Given information

Time period = 28hours=100800s,speed of orbiting =7.5km/s.

02

Calculation

According to the Kepler's 3rd law, the time period is given by T2=4Ï€2R3GM

Where, T is time period, R is the radius of the orbit, G is the universal gravitational constant and M is the required mass of the planet.

Also,v=2Ï€RT

Here, R is unknown and is given by the below formula. v is the speed, R is the radius and T is the time period.

Now solving we get,

v=2πRTR=v×T2πR=(7500m/s)(28×60×60s)2πR=1.203×108m

Now substituting all the values in Kepler's third law equation we get,

T2=4π2r3GMT2=4π2R3GMM=4π2R3GT2M=4π21.203×108m3(6.67×10-11Nm2/kg2)1.008×105kg2M=8.83×1025kg≃1×1026kg

03

Final answer

The mass of the planet is1026kg.

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