What led astronomers to believe in the existence of dark matter? A. the fact that space is black
B. the big bang theory
C. the apparent effects of the gravity of unseen matter on visible objects
D. the existence of black holes

Your pendulum clock which advances 1.0 s for every complete oscillation of the pendulum is running perfectly on earth at a site where the magnitude of the acceleration due to gravity is 9.80 m/s2. you send the clock to a location on the moon where the magnitude of the acceleration due to gravity is 1.65 m/s2.

Player kicks a soccer ball from ground level and sends it flying at an angle of 30 degrees at a speed of 26 m/s. what is the horizontal velocity component of the ball to the nearest tenth of a m/s?

In what direction does the medium move relative to the direction of the wave? explain.