What is the mass of an object that creates 33,750 joules of energy by traveling at 30 meters a second?

What is the name of the perceived change in a sound wave’s frequency due to motion between the observer and the sound source?

What do we mean by the event horizon of a black hole?

Why does lightning travel from clouds to the ground? a. the negatively charged ground attracts the positive charge from the clouds b. charges are exchanged between negatively charged clouds and positively charged ground c. gravity pulls the negatively charged energy from clouds downward d. gravity pulls the positively charged energy from clouds downward