Answer:

Explanation:
M = Mass of each star
T = Time period = 15.5 days
v = Orbital velocity = 230 km/s
G = Gravitational constant = 
Radius of orbit is given by

We have the relation

The mass of each star is 
Gravity is the correct answer.
Answer:
Explanation:
The diagram has a fairly simple explanation. In the top diagram, the space between the particle is increasing. That means that acceleration is increasing. The bottom diagram shows just the opposite. The particle starts off making large "distances" between where the particle is recorded and then the distances between recordings lessens and the particle is slowing down.
Rule: the greater the "distance" between dot positions, the greater the acceleration, because the speed is large.
Top diagram: increasing distance between dots = larger speed. The distance becomes greater as the particle moves to the right.
Bottom diagram: starts off large and decreases as we move from left to right = - acceleration.
Answer:
A. 20 N
Explanation:
Weight of the book = mass × acceleration due to gravity
= 2 × 10
= 20 N