Calculate the orbital speed of an artificial satellite travelling $200 \mathrm{km}$ above the Earth's surface. (The radius of Earth is$6.4\times {10}^6\mathrm{m}$ and its mass is$6.0\times {10}^{24} \mathrm{kg}.$) 

Although some international telephone signals are sent via satellites in geostationary orbits, most are sent along cables on the Earth's surface. This reduces the time delay between sending and receiving the signal. Estimate this time delay for communication via a satellite, and explain why it is less significant when cables are used

(a). Radius of geostationary orbit$=42 300 \mathrm{km}$ 

Although some international telephone signals are sent via satellites in geostationary orbits, most are sent along cables on the Earth's surface. This reduces the time delay between sending and receiving the signal. Estimate this time delay for communication via a satellite, and explain why it is less significant when cables are used radius of Earth $=6400 \mathrm{km}$.

Although some international telephone signals are sent via satellites in geostationary orbits, most are sent along cables on the Earth's surface. This reduces the time delay between sending and receiving the signal. Estimate this time delay for communication via a satellite, and explain why it is less significant when cables are used

(C). speed of electromagnetic waves in free space $\mathrm{c}=3.0\times {10}^8\mathrm{m} {\mathrm{s}}^{-1}$ 

An astronaut is on a planet of mass $0.50{\mathrm{M}}_{\mathrm{E}}$and radius $0.75{\mathrm{r}}_{\mathrm{E}}$, where ${\mathrm{M}}_{\mathrm{E}}$ is the mass of the Earth and${\mathrm{r}}_{\mathrm{E}}$ is the radius of the Earth. 
What is the gravitational field strength at the surface of the planet?

Consider the dwarf planet Pluto to be an isolated sphere of radius $1.2\times {10}^6\mathrm{m}$ and mass of $1.27\times {10}^{22}\mathrm{kg}.$What is the gravitational potential at the surface of Pluto?