Gravitational waves were first detected directly in 2015. According to models, the source of these gravitational waves was . A. a neutron star supernova
B. the merger of two black holes
C. the supernova of an extremely massive star
D. a white dwarf supernova
E. very powerful x-ray bursts

An object weighs 40n in air, weighs 20n when submerged in water and 30n when submerged in a liquid of unknown density. what is the density of the liquid?

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".

If the moon rises at a given location at 6: 00 p.m. today, about what time will it rise tomorrow night?