Which is larger, 65mph or 120kph? as a percentage, how much faster is one than the other?

Curious carl calculated the density of a cube to be 4.50 g/cm3. what is the density of the cube in g/l?

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?

Which best represents the law of conservation of mass ?