Which of the following stars is the coolest?

Which of the following stars is the coolest?
 
  A) B7
  B) G9
  C) K7
  D) K4

Question 2

To determine the height of a flagpole, Abby throws a ball straight up and times it. She sees that the ball goes by the top of the pole after 0.5 s and then reaches the top of the pole again after a total elapsed time of 4.1 s.
 
  How high is the pole above the point where the ball was launched? A) 10 m
  B) 13 m
  C) 16 m
  D) 18 m
  E) 26 m

Question 3

A plane, flying horizontally, releases a bomb, which explodes before hitting the ground. Neglecting air resistance, the center of mass of the bomb fragments, just after the explosion
 
  A) moves vertically.
  B) moves horizontally.
  C) is zero.
  D) moves along a parabolic path.
  E) remains in the plane.

Question 4

Since the Helium molecule (He) is 2 times as massive as the Hydrogen molecule (H2), the speed of sound in Hydrogen is ________ the speed in Helium.
 
  A) 1.41 times
  B) two times
  C) four times
  D) eight times
  E) 1/ times