What is the name for the area of dust and debris which orbited the young sun and eventually became planets and moons? a) intersteller cloud b) oort cloud c) protoplanatary disc d) nebula

A900 kg roller coaster car is travelling westward on the track and begins to slow down from 18m/s to 2m/s. how long does it take the roller coaster car to decelerate if the force acting on the car to slow it is 7024n? how far does the roller coaster travel during this time?

Modern physics a photon emitted from an excited hydrogen atom has an energy of 3.02 electron volts. which electron energy-level transition would produce this photon? a. n=1 to n=6 b. n=2 to n=6 c. n=6 to n=1 d. n=6 to n=2 i chose b but the correct answer is d can someone tell me why? and what's the difference?

Consider a system with two masses that are moving away from each other. why will the kinetic energy differ if the frame of reference is a stationary observer or one of the masses?