C., used in power plants I think.
The answer is D. centripetal force
This definition of centripetal force is a force acting towards the center of an object moving in a circular motion. Acceleration is the rate of which velocity changes over a period of time. If you pick a point on say a rotating circle and find the tangential velocity at each point it goes through, the acceleration would be towards the middle.
I believe it is A. positive acceleration since it is speeding up
Answer:
Acceleration: 
Explanation:
The acceleration of an object is equal to the rate of change of velocity:

where
u is the initial velocity
v is the final velocity
t is the time taken for the velocity to change from u to v
For the space probe in this problem, we have:
u = 100 ft/s (initial velocity)
v = 5000 ft/s (final velocity)
t = 0.5 s (time taken)
Therefore, the acceleration is
