# Orbits

Answer the following questions. Mark on the screen. You may change

#1 The force exerted by the Sun on a solar system planet is

a. a universal constant
b. the same for all planets
c. proportional to the mass of the Sun
d. all of the above
#2 In 1957, the USSR won the first round of the space race by successfully launching the first artificial earth satellite, Sputnik I. The information most vital to the USA at the time was the mass of the payload the USSR was able to launch. After the launch, President Eisenhower asked his science advisors, "All we know for certain about Sputnik is its altitude and orbital speed. From that information can you calculate Sputnikās mass?" The science advisorsā answer was:

a. "Yes, we can."
b. "No, we cannot."
#3 Suppose the earth had no air and were a completely smooth sphere. Could an object be given enough initial velocity so that it could maintain an orbit arbitrarily close to the surface of the earth, as long as it didnāt touch the surface?

a. Yes, it could.
b. No, it couldnāt, because orbits can only occur at altitudes high enough that the force of gravity is reduced.
c. No, it couldnāt, because the period of such a low altitude orbit would be less than the smallest physically possible period.
d. No, it couldnāt, for a reason not stated above.