The first time that astronomers observed both gravitational waves and electro-magnetic waves from the same event, what they were observing was:
a. the merger of two black holes with masses dozens of times the mass of our Sun
b. a supernova explosion in one of the closest galaxies to us
c. the collapse of an entire cluster of stars into one big black hole
d. the spiraling toward each other of two neutron stars
e. a binary star system where a giant star is overloading a white dwarf with too much material

The human body stores chemical energy from digested food. some of the chemical energy is converted into mechanical energy when the body moves. which statement best supported by this information

Ryan is examining the energy of the particles in a bar of gold. what is ryan most likely studying?

Aparticle's position is given by x = 3.00 - 9.00t + 3t2, in which x is in meters and t is in seconds. (a) what is its velocity at t = 1 s? (b) is it moving in the positive or negative direction of x just then? (c) what is its speed just then? (d) is the speed increasing or decreasing just then? (try answering the next two questions without further calculation.) (e) is there ever an instant when the velocity is zero? if so, give the time t; if not, answer "0". (f) is there a time after t = 3 s when the particle is moving in the negative direction of x? if so, give the time t; if not, answer "0".