For what reason did the early Greeks believe the appropriate shape for an orbit was round? Select all that apply. Ptolemy proved that orbits were circular.
Greeks believed the circle represented perfection.
The circular orbit and epicycles allowed for relatively accurate predictions in the placement of the planets.
The earth was known to be round at this time.

You have been hired to design a spring-launched roller coaster thatwill carry two passengers per car. the car goes up a 10-m highhill, then descends 15m to the track's lowest point. you'vedetermined that the spring can be compressed a maximum o 2.0m andthat a loaded car will have a maximum mass of 400kg. for safetyreasons, the spring constant should be 10% larger than the minimumneeded for the car to just make it over the top. a) what spring constant (k) should you specify ? b) what is the maximum speed of a 350 kg car if the spring iscompressed the full amount.