A 40 kg skateboarder runs at a constant velocity of 12 m/s and jumps off a stationary skateboard with a mass of 8 kg. What is the velocity of the skateboard after the jump?

What color would an object that reflects green and blue light appear to be in white light? a. blue b. cyan c. magenta d. black

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?

What is the force that opposes motion and works against the downward pull? a) friction b) gravity c) weight d) acceleration