Physics · Gravitation · NEET
Its period is exactly 24 h, the same time Earth takes to spin once. It also moves in the same direction as Earth's rotation (west to east) and stays above the equator. So the satellite and the ground point below it turn together at the same rate. From Earth it seems fixed at one spot in the sky. This is why a dish antenna can point at it once and never move again.
Height is about 36,000 km (roughly 35,786 km) above Earth's surface. Its period T = 24 h = 86400 s. You get this height from T^2 = (4 pi^2 / GM) r^3. Solving for r gives about 42,000 km from Earth's centre, and subtracting Earth's radius (about 6,400 km) leaves about 36,000 km height. NEET expects you to remember 36,000 km and 24 h.
Not exactly. A geosynchronous satellite has a 24 h period but its orbit can be tilted, so it traces a small figure-8 in the sky. A geostationary satellite is a special geosynchronous one that also lies in the equatorial plane and moves west to east, so it stays truly fixed over one point. Every geostationary satellite is geosynchronous, but not every geosynchronous satellite is geostationary.
Polar satellites are used for imaging, weather and mapping, so they need a close, detailed view of the surface. A low orbit (about 500 to 800 km) gives sharper images and a short period (about 100 min), so the satellite completes many orbits per day. As Earth rotates below its polar path, the satellite slowly covers strips of the whole planet, including the poles that a geostationary satellite can never see.
No. A geostationary satellite must sit in the equatorial plane, so it can only stay fixed above a point on the equator, not above Delhi or any pole. To watch the poles you need a polar satellite. This is a favourite NEET trick, so remember: geostationary = equator only.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
About 3.1 km/s. Because it is very high (r about 42,000 km from centre), its speed v = sqrt(GM/r) is small compared with a low satellite. A low polar satellite moves much faster, about 7.5 to 7.8 km/s, since it is close to Earth.
A minimum of 3, placed 120 degrees apart around the equator. Together they can relay signals to almost all of the populated Earth, though the polar regions stay in a blind spot.
It stays in the equatorial plane, always above the equator. From that fixed spot the curved Earth blocks the view of the poles, so weather and mapping over the poles must use polar satellites.
No. A polar satellite moves fast in a low orbit with a period of about 100 min, so it rises and sets many times a day. It does not stay fixed like a geostationary satellite.
Use T^2 = (4 pi^2 / GM) r^3 with T = 86400 s. Solve for r, then height h = r - R where R is Earth's radius. This gives r about 42,000 km and h about 36,000 km.
