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Time Period of Counter Orbiting Equatorial Satellite

A geostationary satellite above the equator is orbiting around the earth at a fixed distance r1r_1 from the center of the earth. A second satellite is orbiting in the equatorial plane in the opposite direction to the earth's rotation, at a distance r2r_2 from the center of the earth, such that r1=1.21 r2r_1 = 1.21\ r_2. The time period of the second satellite as measured from the geostationary satellite is 24p\frac{24}{p} hours. The value of pp is ___

Official Numerical Answer2.3 to 2.4

Step-by-Step Solution

The time period of a geostationary satellite orbiting the Earth is equal to the rotational period of the Earth: T1=24 hoursT_1 = 24 \text{ hours}

According to Kepler's Third Law, the time period of a satellite in a circular orbit around the Earth is related to its orbital radius rr by: T2r3    Tr3/2T^2 \propto r^3 \implies T \propto r^{3/2}

Therefore, the ratio of the time periods of the second satellite (T2T_2) and the geostationary satellite (T1T_1) is: T2T1=(r2r1)3/2\frac{T_2}{T_1} = \left(\frac{r_2}{r_1}\right)^{3/2}

Given that r1=1.21r2r_1 = 1.21 \, r_2, we have: r2r1=11.21=1(1.1)2\frac{r_2}{r_1} = \frac{1}{1.21} = \frac{1}{(1.1)^2}

Substituting this into the ratio: T2T1=(1(1.1)2)3/2=1(1.1)3=11.331\frac{T_2}{T_1} = \left(\frac{1}{(1.1)^2}\right)^{3/2} = \frac{1}{(1.1)^3} = \frac{1}{1.331}

So, the time period of the second satellite with respect to the Earth's center is: T2=241.331 hoursT_2 = \frac{24}{1.331} \text{ hours}

The angular speeds of the two satellites with respect to the Earth's center are: ω1=2πT1\omega_1 = \frac{2\pi}{T_1} ω2=2πT2\omega_2 = \frac{2\pi}{T_2}

Since the second satellite orbits in the equatorial plane in the direction opposite to the geostationary satellite, their relative angular velocity as seen from the geostationary satellite is the sum of their individual angular velocities: ωrel=ω1+ω2=2πT1+2πT2\omega_{\text{rel}} = \omega_1 + \omega_2 = \frac{2\pi}{T_1} + \frac{2\pi}{T_2}

The time period of the second satellite as measured from the geostationary satellite (TrelT_{\text{rel}}) is given by: Trel=2πωrel=11T1+1T2T_{\text{rel}} = \frac{2\pi}{\omega_{\text{rel}}} = \frac{1}{\frac{1}{T_1} + \frac{1}{T_2}}

Given Trel=24pT_{\text{rel}} = \frac{24}{p} hours, we set up the equation: 24p=1124+1.33124=241+1.331=242.331\frac{24}{p} = \frac{1}{\frac{1}{24} + \frac{1.331}{24}} = \frac{24}{1 + 1.331} = \frac{24}{2.331}

Equating the denominators: p=1+1.331=2.331p = 1 + 1.331 = 2.331

Rounding off to two decimal places gives: p2.33p \approx 2.33

Time Period of Counter Orbiting Equatorial Satellite | Physics PYQ Solution - JEE Challenger